8 



Transactions. 



prothallus is more opaquely brown than that of the rhizome, the latter 

 appearing a clearer golden brown, with its surface cells outlined with great 

 distinctness, this difference in appearance being due possibly to the denser 



fungal element in 

 the interior tissues 

 of the prothallus. 

 The older basal 

 regions of the pro- 

 th alii are often 

 darkly brown in 



Fig, 5. — Complete branched pro- 3 

 thallus of large size, bearing^] 

 young plant which "shows \ 

 both rhizome and aeri 

 stem, x 3. 



Si WF" p 



colour or even blackish, owing 

 not so much to any withering- 

 away of the tissues as to the 

 presence of the mycorhiza 

 in this region in the cells 

 immediately underlying the Q. 

 epidermis, and, in the oldest 

 regions of all, in the epidermal 

 cells also, as well as in those 

 more centrally situated. 



The prothallus in trans 

 verse section is round in out 

 line (figs. 16 and 17), this 



being so throughout its length, so that its construction is consistently 

 radial. Its growth in length is referable to the activity of a single 

 cell (figs. 20 and 21), such as is the case also with the cylindrical pro- 

 thalli of the Ophiogk ssaceae. A transverse section through the main 



Fig. 6. — Complete branched prothallus of large size, 

 one main branch showing further irregular 

 branching, x 10. 



