Hollow at. — The Prothallus and Young Plant of Tmesipteris. 



may be seen sometimes in the lower regions of the latter (fig. 5), indicating 

 that the growth of the prothallus is by no means arrested by the develop- 

 ment on it of a plant, but may go on after the latter has attained a 

 considerable size or has even become detached from the prothallus. 



When first seen amongst the tangle of black aerial rootlets of the tree- 

 fern stem the prothalli may easily be mistaken for broken portions of 

 the rhizome of young plants or for very young complete isolated plantlets, 

 and vice versa. Both the prothalli and the rhizomes are brown in colour, 

 and both are covered fairly thickly with the long yellow-brown rhizoids 



Fig. 2. — Complete prothallus, carrot form, commencing to fork, bearing young 



plant, x 9. 

 Fig. 3. — Prothallus, carrot form, original end broken off, showing swollen head. X 12. 

 Fig. 4. — Prothallus, branched, one branch broken off, shows original end intact, 



also point of attachment of young plant, x 12. 

 Fig. 4a. — Original end of prothallus shown in fig. 4. x 36. 



or with the characteristic small brown circles formed by the persisting 

 bases of broken-ofi rhizoids. The similarity holds also with regard to their 

 growing apices, which are always somewhat swollen and are clear and 

 whitish in appearance and show rhizoids only in their earlier stages of 

 development. Each object dissected out has generally to be separately 

 cleaned and examined under a low power of the microscope before its 

 nature can be definitely determined. This is especially so in the case 

 of the branched prothalli, whereas the carrot - shaped individuals are 

 more easily recognized. However, generally speaking, the colour of the 



