JUDGMENT Balakrishna Eradi, C.J. 1. The judgment of the Court was delivered by Balakrishnan Eradi, C. J. - The petitioners in these two writ petitions are two employees of the establishment attached to the office of the Accountant General, Kerala. Both of them are holding substantively the posts of Section Officers. The petitioner in O. P. No. 3400 of 1979 is temporarily on deputation to the Lotteries Department of the State Government, but his substantive lien is in post of Section Officer in the Indian Audit and Accounts Department in the office of the Accountant General, Trivandrum. The challenge in both these writ petitions is primarily against the constitutionality of the circular, dated 25th February 1973. Ext. P2 issued by the Comptroller and Auditor General, New Delhi, wherein inter alia it has been directed that while effecting promotions in the Audit and Accounts Department from Class III posts to Class II posts a reservation to the extent 15 per cent for Scheduled Castes and 7 1/2 per cent for Scheduled Tribes will have to be made with reference to the number of posts of Accounts Officers to be filled up each year by promotion to be effected on the basis of seniority subject to fitness. The petitioner in O.P. No. 3388 of 1979 has prayed for the issuance of direction to respondents Nos. 1 to 3 namely Union of India. The Comptroller and Auditor General of India, New Delhi and the Accountant General of Kerala, Trivandrum, respectively to make promotions to the cadre of Accounts Officers without reference to the instructions contained in the circular Ext. P2 and to refrain from giving any preference to the respondents Nos. 4 to 6 who belong to Scheduled Castes, in the matter of promotion to the cadre of Accounts Officers on the basis of the provision for reservation contained in Ext. P2. In O.P. No. 3400 of 1979 the petitioner, besides seeking to quash the circular Ext. P2, has prayed that the promotions already granted to respondents Nos. 4 to 11 there in should be declared illegal and void. Respondents Nos. 4 to 10 were promoted on the basis of the reservation provided for in Ext. P2 all of them being persons belonging to Scheduled Castes. P2, has prayed that the promotions already granted to respondents Nos. 4 to 11 there in should be declared illegal and void. Respondents Nos. 4 to 10 were promoted on the basis of the reservation provided for in Ext. P2 all of them being persons belonging to Scheduled Castes. Respondent No. 11 was promoted on the basis of his having been selected by the Departmental Promotion Committee to the quota reserved for promotion on the basis of selection with reference to merit and ability. 2. The main contention advanced on behalf of the petitioners in support of the challenge raised by them against circular Ext. P2 is that the offending provision contained in Ext. P2 has really the effect of modifying the statutory rules framed by the President of India under the proviso to Art.309 of the Constitution. Ext. P1 is a copy of the aforementioned rules, which are called 'the Indian Audit and Accounts Department (Administrative Officers) Assistant Accounts Officers and Assistant Audit Officers, Recruitment Rules, 1963'. It is contended by the petitioners that under Clause.5, 10 and 11 of Ext. P1 all the personnel in the category of Section Officers had been conferred entitlement to promotion to the immediate higher category of Accountants on the basis of their seniority subject to fitness and that a substantial inroad has been made in to this right by the provision for reservation of 22 1/2 per cent of the vacancies in favour of Scheduled Castes and Scheduled Tribes candidates made as per the circular Ext. P2, which is only an executive order. Counsel for the petitioners strongly urged before us that it was not open to the Auditor General of India to modify the statutory rule by issuing an executive order especially when the power to make rules was vested with the President of India under Art.148(5) of the Constitution. 3. On the side of the respondents the aforesaid argument was sought to be met by submitting that the statutory rules contained in Ext. P1 do not at all deal with the subject as to how the promotions are to be effected to the quota of 50 per cent which was to be treated as non selection posts and the rules being silent in respect of this matter, it was perfectly competent to the Auditor General of lndia to fill up the gap by issuing executive instructions. In this context the learned Central Government Pleader pointed out to us that the procedure to be adopted for effecting promotions to the 50 per cent quota of non selection posts in the category of Accountants was laid down by administrative instructions issued by the Comptroller and Auditor General of India and incorporated in the Comptroller and Auditor General's Manual of Standing Orders as Para.160. Our attention was also drawn to the fact that prior to the issuance of Ext. P2 there had been an earlier circular issued by the Comptroller and Audit General of India on 3rd October 1968 touching the subject of reservation of posts in favour of Scheduled Castes and Scheduled Tribes candidates and it. was in modification of the said circular, in view of an alteration in the Government of India's policy in that regard that the impugned circular Ext. P2 came to be issued. Ext. R1 produced along with the counter affidavit filed in O. P. No. 3400 of 1979 is a copy of the earlier circular issued by the Auditor General of India on 3rd October 1968. 4. Counsel appearing for the private party respondents in both the writ petitions also strongly supported the aforesaid contentions put forward by the Central Government Pleader. In addition, it was pointed out by the counsel for such respondents in O. P. No. 3400 of 1979 that the respondents Nos. 4 to 10 therein had been promoted under various orders passed during the period from 27th July 1976 to 8th June 1978 and the challenge raised by the writ petitioner against those promotions in this writ petition, which was presented to this court on 9th October 1979 is most highly belated and it has to be rejected on that said preliminary ground itself. It was further submitted by the counsel appearing for the respondents that the promotion given to respondent No. 11 was not based on the circular Ext. P2 but was founded on his having been selected by the Departmental Promotion Committee in the quota of 50 per cent reserved for selection on the basis of merit and ability and hence there is absolutely no valid ground on which the petitioner, who was not found suitable by the Departmental Promotion Committee for inclusion even in the preliminary select list, can challenge the said promotion, 5. The main plank of attack of the petitioners in both the cases being that Ext. P2 is inconsistent with the provisions contained in the statutory rules evidenced by Ext. P1 and is invalid on that account, we shall straightaway proceed to examine the relevant provisions contained in Para.5, 10 and 11 in the schedule to Ext. P1, which alone arc relied on by counsel for the petitioners. Clause.5 in the schedule to Ext. P1 reads: "Whether selection post or non-selection post 50 per cent of the posts are selection posts and the      remaining 50 per cent are non-selection posts." The name of the post concerned has been given in Clause.1 of the schedule as Administrative Officer / Assistant Accounts Officer / Assistant Audit Officer in the Indian Audit and Accounts Department. Clause.10 and 11 read as hereunder:" "10. Method of recruitment whether by direct recruitment or by promotion or transfer and percentage of the vacancies to be filled by various methods. By promotion 11. In case of recruitment by promotion/transfer, grades from which promotion /transfer to be made Promotion-Subordinate accounts service/Subordinate Railway Audit Service Cadres." Clause 5 goes only to the extent of declaring that 50 per cent of the posts of Assistant Accounts Officers (now redesignated as Accounts Officer) are to be treated as selection posts and the remaining 50 per cent as "non selection" posts. The combined effect of Clause.10 and 11 is to lay down that all the posts shall be filled up by promotion to be effected from amongst the members of two cadres, namely the Subordinate Accounts Service and the Subordinate Railway Audit Service. There is thus, no specification whatever in Ext. P1 as to how appointments arc to be made by promotion to the 50 per cent non selection posts. The rules are totally silent on the said subject. It is only by administrative instructions incorporated in Para.160 of the Comptroller and Auditor General's Manual of Standing Orders that detailed provision was made as to how the promotion to the said 50 per cent of the vacancies was to be effected. That paragraph reads: "160. The rules are totally silent on the said subject. It is only by administrative instructions incorporated in Para.160 of the Comptroller and Auditor General's Manual of Standing Orders that detailed provision was made as to how the promotion to the said 50 per cent of the vacancies was to be effected. That paragraph reads: "160. Promotion to 50 per cent of the vacancies in the grades of Accounts / Audit Officers is made by selection on the basis of merit from amongst the eligible members of the Subordinate Accounts Service / Subordinate Railway Audit Service who have outstanding very good record and the selection is made irrespective of seniority and limited to the number of such persons available. Promotion to the remaining 50 per cent or more vacancies is made on the principles of seniority cum fitness from amongst the eligible persons. The members of the Subordinate Accounts Service / Subordinate Railway Audit Service are required to satisfy such conditions as are imposed by the Comptroller and Auditor General from time to time before they are considered eligible or fit for promotion e.g. proficiency in Revenue Audit for members of the Subordinate Accounts Service (Ordinary Brach)." It was when matters stood thus that, consequent on a change of policy decided by the Government of lndia with respect to the making of special provisions for reservation in favour of Scheduled Caste and Scheduled Tribes candidates to promotion posts, after consultation with the Comptroller and Auditor General, a decision was taken by the Central Government to extent the same principle to the personnel serving in the Audit and Accounts Department. It was in implementation of the said decision that the impugned circular, Ext. P2, was issued by the Comptroller and Auditor General in modification of his earlier circular evidenced by Ext. R1. There cannot be any doubt that the making of a provision for reservation of appointment or posts in favour of persons belonging to Scheduled Castes and Scheduled Tribes is a matter having an intimate beating on the mode of making appointments and promotions to posts in the service of the State. As we have already seen, the rules contained in Ext. As we have already seen, the rules contained in Ext. P1 are completely silent as to the manner in which promotions are to be effected to the 50 per cent of the posts of Accounts Officers declared thereunder as non selection posts and the procedure in respect of the matter was governed only by the administrative instruction issued as per Para.160 of the manual already referred to. Mention has also been made of the fact that on the specific subject of reservation of posts in this department in favour of Scheduled Castes and Scheduled Tribes candidates there was a prior executive circular issued by the Auditor General as per Ext. R1. Under that circular no reservation had been provided for in respect of posts to be filled up by promotion based on seniority subject to fitness. It was in modification of the said circular that revised instructions were issued by the Auditor General as per Ext. P2, directing that there shall be a reservation to the extent of 15 per cent in favour of Scheduled Castes candidates and 7 1/2 per cent in favour of Scheduled Tribes candidates in filling up posts by promotion on the basis of seniority subject to fitness. Such a direction is fully within the scope of the enabling power conferred by Clause.(4) of Art.16 of the constitution. It is now well established that the special provision referred to in Art.16(4) need not necessarily be made by legislation and that it can be made by executive orders passed by the concerned Government (Union or State) - see Trilok Nath v. State of J. and K. AIR 1969 SC 1 . It is equally well established that where statutory service rules are silent in regard to any particular aspect concerning service conditions, the said gap can be filled in by administrative and executive orders - see B. N. Nagarajan v. State of Mysore AIR 1966 SC 1942 and Ram v. State of Rajasthan AIR 1967 SC 1910 . In the light of the conclusion reached by us that Ext. P1 is silent in regard to the manner in which promotions are to be effected to 50 per cent of the posts of Accounts Officers which are declared as non selection posts and that what has been done under Ext. P2 is only to make a provision in supplementation of what is contained in Ext. P1 is silent in regard to the manner in which promotions are to be effected to 50 per cent of the posts of Accounts Officers which are declared as non selection posts and that what has been done under Ext. P2 is only to make a provision in supplementation of what is contained in Ext. P1 with respect to a matter not dealt with in it, there cannot be of any question of inconsistency between Ext. P2 and Ext. P1. The argument of the petitioners that Ext. P2 which is an executive order has purported to modify the provisions contained in Ext. P1 which are statutory in origin cannot therefore be sustained. We have no hesitation to reject the challenge raised by the petitioners against Ext. P2 as being devoid of any merit. 6. The respondents in O.P. No. 3400 of 1979 arc also on the strong ground in the contention put forward by them that the said writ petition in so far as it has questioned the legality and validity of the promotions given to respondents Nos. 4 to 10 is hopelessly belated. The delay was sought to be explained by counsel for the petitioner by submitting that the petitioner was on deputation to the Lotteries Department of the State Government. But this submission omits to take note of the fact that admittedly the petitioner went on deputation only on 10th June 1977, whereas the promotions to the respondents Nos. 4 and 5 had been effected even as early as on 27th July 1976 and 7th April 1977 respectively. Besides, we find it difficult to believe that the petitioner who was attached to the Office of the Director of Lotteries situated in Trivandrum itself would have been totally unaware of the factum of the promotions given to respondents Nos. 4 to 10 for a period of more than two years after the date of effecting those promotions so as to entitle him to contend that it is his ignorance of the said fact that prevented him from approaching this court for relief within a reasonable time. 7. Coming to the challenge raised by the petitioner in O.P. 3400 of 1979 against the promotion given to respondent No. 11, he is not a candidate belonging to the Scheduled Castes or Scheduled Tribes. 7. Coming to the challenge raised by the petitioner in O.P. 3400 of 1979 against the promotion given to respondent No. 11, he is not a candidate belonging to the Scheduled Castes or Scheduled Tribes. It is seen from the counter affidavits filed on behalf of the respondents that respondent No. 11 was promoted on the basis of his having been selected by the Departmental Promotion Committee for promotion in the 50 per cent quota declared as selection posts and that the petitioner, though considered by the Departmental Promotion Committee, had not been selected by it. The Central Government Pleader placed before us for our perusal the confidential records of the petitioner and the 11th respondent as well as the minutes of the Departmental Promotion Committee which had met in 1978. After going through those records we are perfectly satisfied that there is absolutely no merit in the contention put forward by the petitioner that the selection made by the Departmental Promotion Committee was arbitrary. It then follows that the challenge raised by the petitioner against the promotion of 11th respondent has also to fail. 8. The conclusion that emerges from the foregoing discussion is that the petitioners are not entitled to any of the reliefs prayed for in the petitioners. The Original Petitions are accordingly dismissed, but, in the circumstances, without any order as to costs.