224 A FREE-LIVING SPOROPHYTE 



each season's growth, while the tuber itself is here greatly enlarged for 

 purposes of storage. The characteristic "protocorm" is absent from all 

 other Pteridophytes. 



The question is, what is the true interpretation of these facts. Does 

 the protocorm really represent some condition which existed in the 

 phylogeny, intermediate between the fully-rooted sporophyte and that 

 more primitive state where it was fully dependent on the prothallus? 

 The first point which strikes attention is the way in which the transition 

 from dependence to independence of the sporophyte is actually carried 

 out in the plants which show this " protocorm " development : assuming 

 that there is some difficulty, nutritive or other, in formation of the root 

 itself, the case is quite adequately met by the tuberous development with 

 rhizoids, as a temporary shift. It seems not improbable that some such 

 difficulty should precede in descent the initiation of so important, and so 

 characteristic a body as the root. A second point, however, is that a 

 protocorm development is exceedingly limited in its distribution among 

 living plants : it is not constant even in the genus Lycopodium^ and 

 outside the Lycopodiales it is not characteristically developed in any 

 other of the early forms : this must be taken fully into consideration 

 before assigning to the " protocorm " any general phyletic significance. 

 But, on the other hand, it may be urged that the real importance of 

 the " protocorm " would exist only in those cases where either the 

 root-development has not yet been initiated in the race, or where its 

 late development in the individual is a matter of moment, on nutritive 

 or other grounds. Immediately any initial difficulty of development of 

 a root-system is surmounted in any line of descent, the " protocorm " 

 would be liable to be cut out of the ontogeny, as a cumbrous and 

 unnecessary stage. This would sufficiently account for the absence of a 

 " protocorm " in the great majority of Vascular Plants. But, again, 

 Goebel, in arguing against the general phyletic significance of a 

 " protocorm," has cited a number of cases of Phanerogamic Plants in 

 which, if the formation of the root is suppressed temporarily or entirely 

 in the seedling, a protocorm-like body is formed, which is anchored to 

 the substratum by hairs. 1 He remarks that this appearance of a 

 protocorm in very different circles of affinity seems to him unfavourable 

 to the hypothesis of its having a phyletic significance, and he only sees 

 in it an organ which corresponds in its development, and especially in 

 its formation of roots, to an arrested hypocotylous segment : he suggests 

 that a suppression of the formation of the roots may have taken place 

 in Lycopodium, as also in the Orchideae, and that this was connected 

 with the prolonged development of the germ-plant in them : perhaps 

 also the symbiosis with fungi which takes place in these plants, may 

 have had its effect. On this view the " protocorm " would be secondary, 

 and it would not illustrate an archaic mode of establishment of the 

 1 Organography, vol. ii., Engl. ed., p. 232 



