208 



Transactions. 



that in this particular figure the hinder region of the prothallus is not cut 

 longitudinally, so that although the fungal tissue in the figure seems to bear 

 some relation to the meristem this is really not the case. In the branches 

 in which the fungus is found almost throughout the entire length it is absent 

 from the whole of the tip of the branch, even in the case of the " resting " 

 processes which are so packed with fungus (fig. 32). Thus the growing tips 

 always appear clear and translucent. A lateral branch arises adventitiously 

 on the central prothallial body by one or more of the externally-placed 

 cells of the latter setting up a local meristem. This can be seen from 

 fig. 33, which shows in longitudinal section a very young lateral branch 

 being formed alongside some old paraphyses. At first the process extends 

 in length by the activity of a single triangular apical cell (fig. 33), but 

 probably very early the apex broadens and more than one cell becomes 

 meristematic. , Miss Edgerley states that at the tips of the branches she 

 found two initials (4, p. 105). 



Relation of the Young Plant to the Prothallus. 



In the epiphytic species, whereas the antheridia are frequently borne on 

 certain parts of the lateral branches as well as on the central body of the 

 prothallus, the archegonia are borne on the latter only. At the same time, 

 it will be remembered that this central body may not have grown directly 

 from the germinating spore, but may have originated by the development 

 of a detached branch. This central body of the prothallus, as has been 

 described, consists of a hinder vegetative region and a forward more bulky 

 generative region, and it is to the latter that the young plant is attached 

 (figs. 1, 6, 7, 11, 34, 36, 37). Not infrequently more than one developing 

 plantlet is attached to the same prothallus (fig. 37). 



V 



35 



Figs. 35-37. — L. Billardieri var. gracile. Prothalli bearing one or more 

 young plants, in general view. Fig. 35, x 3 ; figs. 36 and 37, X 6. 



The prothallus, being placed well below the surface of the humus, is 

 called upon to nourish the young plant altogether until the latter can reach 

 the surface and produce its first leaves. The naked stems of the developing 

 plantlets are sometimes as much as | in. long before they reach the light. 

 In accordance with this considerable degree of dependence of the young 

 plant upon its parent prothallus, that part of the base of the plant which 

 is in contact with the prothallial tissues functions as an absorbing " foot." 

 This foot is a well-marked feature m the plantlets of the epiphytic species, 

 although it does not there assume so large a size as it does in the plantlets 



