CHAPTER XXVI. 



EMBRYOLOGY OF THE LYCOPODIALES. 



(A) ELIGULATE LYCOPODIALES. 



IN Chapter XIV. the modern aspect of comparative embryology of the 

 sporophyte has been discussed. For reasons there stated it was concluded 

 that only a minor place in comparisons is to be conceded to the details 

 of the initial embryology of the sporophyte : the characteristic form of 

 the mature plant, established after the earlier and in considerable degree 

 adaptive phase of development is past, is held to give a more reliable 

 basis for argument than does the embryonic state. Especially is this the 

 case among the Pteridophyta, and it happens that the Lycopods supply 

 examples of peculiar interest in relation to such questions ; they will serve 

 at once as an illustration, and as a test of the principle thus briefly 

 stated. For in the general conformation of their mature sporophyte there 

 is - a remarkable uniformity throughout the whole phylum : the differences 

 are those of secondary detail : the main facts of plan and proportion of 

 their srioot- and root-systems, of their branching, and of the relation of 

 the sporangia to the other parts, leave no doubt of a natural affinity as 

 based on the character of the mature sporophyte. But in the embryology 

 there are points of marked divergence, which may be more or less clearly 

 correlated with differences of character of the parent prothallus. There is 

 reason to think that within the genus Lycopodium the prothallus and embryo 

 have undergone a cognate divergent development from a central type, 

 though the mature sporophyte has still retained a substantial uniformity. 



The differences in character of the prothallus within the genus Lycopodium 

 are found to be those of habit and of mode of nutrition rather than of 

 fundamental structure. According to their mode of life three main types 

 may be distinguished, which, however, graduate into one another in such 

 a way as to suggest their intimate connection by descent from some 

 common source. The type shown by L. cernuum t and shared also by 

 L. inundatum and sa/akense, consists of a massive cylindrical thallus, of 

 which the conical lower part is sunk in the soil, while ^the upper part is 



