12 



T fa nsact ion s . 



food, contents in its cells, the head of the prothallus forks and the carrot 

 form gives place to the branched form characteristic of the full-grown 

 individuals. 



The Distribution of the Sexual Organs. 



There is no differentiation of the prothallus into vegetative and repro- 

 ductive regions, such as is usual,- for example, in the terrestrial forms 

 of Lycopodium prothalli. The sexual organs are distributed over the sur- 

 face of the whole prothallus-body in large numbers, and often in groups. 

 A transverse section of the limb of a prothallus will often show either 

 antheridia or arcliegonia distributed more or less all around the surface 

 (figs. 16 and 17). The sexual organs are for the most part more inter- 

 mingled than is the case in the branched prothalli of the epiphytic 

 lycopodiums, and correspond in this particular rather to the prothallus of 

 Ophioglossum (Campbell, 1911, p. 10). 



The young developing sexual organs are to be found immediately 

 behind the growing apex of the prothallus, but also, as is known to 

 be the case in 02Jhioglossum (ibid., p. 29), they frequently arise much 

 farther back from it amongst old organs. As a rule, however, both the 

 antheridia and the archegonia arise immediately behind the growing apices 

 in acropetal succession. In nearly every prothallus I noticed developing 



antheridia on the growing branches, 

 in some cases the youngest being 

 fairly close behind the actual apex, 

 whilst in others (where possibly the 

 growth in length of the branch was 

 taking place more rapidly) at a greater 

 distance back from it. In only a 

 very few out of the large number of 

 prothalli found by me were groups 

 of young archegonia to be seen close 

 behind the apex. This fact, however, 

 is probably due to chance only, for 

 archegonia always occur in large num- 

 bers on the main prothallus-body, 

 though the tendency to grouping is 

 more to be remarked in the distribu- 

 tion of the archegonia than of the 

 antheridia. It may possibly be that 

 the archegonia arise in an irregular 

 manner on older parts of the pro- 

 thallus more frequently than do the 

 antheridia. In several instances of 

 adult prothalli (figs. 1, 2, and 3) where 

 growth had slackened, old archegonia 

 were present in fairly large numbers 

 close behind the apex. 

 In the very young prothalli shown in figs. 1 1 and 12 it will be seen that 

 the sexual organs begin to develop comparatively early, and that it is 

 the antheridia that are first formed. The basal regions of older prothalli 

 also generally show the presence of old antheridia. In surface appearance 

 the young developing antheridia are seen as colourless hemispherical pro- 

 turberances (figs. 6, 12, 13, &c). This is generally one of the most 



Fig. 13. — Young complete prothallus, 

 showing swollen bead, sexual 

 organs, and original end. X 16. 



l'lii. 13a. — Original end <>f prothallus 

 shown in fig. 13. > 3(1. 



