Transactions. 



Fig. 



Fro. 



branches had developed into the main prothallus-body, whilst the other 

 had either broken away or persisted towards the base of the first in 

 a state of arrested growth (figs. 4, 5, 6). The forking generally seems 



to result at first in two equal 

 apices of growth (figs. 1, 2), and 

 hence may be termed dichotomous, 

 and, except in the case of the first 

 branching as just described, which 

 takes place when the prothallus 

 is still comparatively small, the 

 resultant branches become more 

 or less equally developed (figs. 2 

 and 5). Hence in most adult 

 prothalli found the original simple carrot- 

 shape form had been lost, and the prothallus 

 had become more irregular in appearance, 

 L dp such as is generally the case with epiphytic prothalli. 

 Thus in this respect the prothalli of T mesipteris can 

 be compared with those of the epiphytic species of 

 Lycopodium and Ophioglossum. In a few instances, 

 moreover, such as those illustrated in figs. 6 and 66, 

 a still greater irregularity of form had been brought 

 about through the branching not taking place dicho- 

 tomously. In the former of these two prothalli the 

 forking seems to have been trichotomous. Still another 

 irregularity in the form of adult prothalli is brought 

 about by the equal development of both 

 daughter branches at the first forking of the 

 prothallus, not, as is usually the case, at an 

 angle to one another, but in directions dia- 

 metrically opposite (fig. 7). This is still more 

 pronounced in the case of the large prothallus 

 shown in fig. 8, in which one of the branches 

 resulting from the first forking had forked 

 again, the two branches of this second forking 

 proceeding to develop in opposite directions 

 ].— Complete prothallus, carrot to one another in the same straight line, 

 form, bearing young plant. Thus the branched form of the adult pro- 

 thallus is attained normally by the dichoto- 

 mous forking of the apex, but I observed also 

 a few instances in which short undeveloped 

 branches had arisen apparently laterally. 

 However, even in the most irregularly shaped adult individuals the manner 

 of growth can always be easily traced, for even if the original long-drawn- 

 out point be not preserved, yet the oldest region can always be dis- 

 tinguished from the rest of the prothallus by its darker brown or even 

 almost black colour. 



On some of the prothalli a large cup-shaped prominence with an 

 obviously lacerated rim was to be seen (figs. 4 ard 73). This is where 

 a young plantlet had been broken away, the cup-shaped prominence 

 having been formed by the localized outward growth of the prothallial 

 tissues around the embryo and their final rupture by the developing 

 plantlet. Such a point of attachment of the plant to its parent prothallus 



, and showing original end intact. 



X 10. 

 1a. — Original end of prothallus 



shown in fig. 1. X 24. 



