THE EMBRYO 



39 



single axial vascular bundle traverses the whole of the young sporophyte without 

 interruption, and there is no recognizable boundary between the tissues of the leaf 

 base and those of the root. The central region of the embryo is somewhat thickei 

 and its outer cells are enlarged, these outer cells probably belonging to the foot 

 through which the root has penetrated and which at this period can not be clearly 

 recognized. The strictly bipolar character of the young sporophyte and the way 

 in which it perforates the gametophyte resemble most nearly the corresponding 

 stages of Equisetum and the Marattiaceae, and it may be said that Lyon's recent 

 studies on Botrychium obliquum indicate that in this species also there is a similar 

 bipolar arrangement of leaf and root. 



Mettenius pointed out in O. pedunculosum that the definitive sporophyte arises 

 as an adventitious bud upon the primary root, either close to the leaf base or, more 

 commonly, at some distance from it. This is also the case in O. moluccanum and 

 the other allied species. In one case observed by me two independent sporophytes 

 were found growing from the same prothallium, but this is unusual, and in most of 

 the cases where two sporophytes seem to be present, one of these is really the sec- 

 ondary sporophyte growing from the primary root. 



Fig. 23. — Ophioglossum moluccanum. 



A. Young cotyledon, longitudinal section; pr, gametophyte. X80. 



B. Apex of cotyledon more highly magnified; x, apical cell. 



C. Young sporophyte in which a rudimentary second leaf (/") is present. X80. 



D. Cross-section of apex of primary root. X200. 



While in 0. vulgatum the sporophyte stays under ground for several years, 

 in 0. moluccanum there is every reason to believe that there is only a brief interval 

 between the first formation of the leaf and its appearance above ground. The small 

 size and the character of the gametophyte, as well as the quick germination of the 

 spores and the rapid growth natural to a tropical climate, indicate that the gameto- 

 phyte is an annual and that it dies as soon as the young sporophyte is established. 



In O. pendulum the primary root as it breaks through the prothallium elongates 

 rapidly, but just how far it grows before the bud is formed upon it could not be 

 determined. These roots are very brittle and easilv broken off, and in no cases were 

 young buds found upon roots which were still connected with the prothallium. The 

 first root sometimes reaches a length of 3 or 4 centimeters before the second root can 

 be seen at all. The growth of the roots in the young sporophyte is in all respects 

 like that occurring in the older ones. There is a large tetrahedral apical cell, the 

 divisions of which are quite regular, and the conspicuous axial vascular cylinder is 



