220 Transactions. 



similarity in general appearance to the surface - growing forms of the 

 L. Selago prothallus, or they may be so irregularly extended in length that 

 their build is difficult to distinguish. In the elongated forms, along with 

 the development of a number of fungal areas, there goes a corresponding 

 development of several distinct generative regions bearing sexual organs 

 and filamentous or lobe-like processes. Frequently, in this latter form 

 of prothallus, the first-formed generative regions are brown and withered, 

 suggesting that the prothallus had resuni^d growth on one or more occa- 

 sions at the close of a dry period or on account of there being no embryo 

 developed. I have always found that a young plant when present was 

 borne on the last-formed region of the prothallus, so that growth in length 

 is apparently not continued after the development of a young plant. The 

 prothalli sometimes persist attached to the developing plant for a much 

 longer time than in L. cernuum. I have found several instances of a healthy 

 prothallus still attached to a plantlet which showed as many as seven or 

 eight protophylls along an extended protocorm. The lateral processes are 

 sometimes filamentous, and at others short and lobe-like. Owing to the 

 fact that the prothallus of L. ramulosum is so variable in form, it is 

 impossible to give many details in a general description of it. I will now 

 proceed to enter more into detail in connection with the particular 

 individuals figured in this paper. 



The prothallus shown in fig. 50 and in Plate XII possessed five fimgal 

 areas, quite distinct from one another, each being swollen and rounded in 

 form and bearing a group of rhizoids. There are two generative regions 

 showing the presence of archegonia and bearing filamentous processes. The 

 basal fungal swelling bore no evidence of any original filamentous stage, and 

 was probably formed immediately on germination of the spore. As wiU 

 be described later, a first-formed filamentous stage is frequently to be 

 observed in the prothalli of this species. The uppermost fungal region is, 

 of course, the youngest. It occurs at the base of the meristematic apex 

 of the prothallus, and it is evident that both this growing apex and its 

 fungal region have just begun to form. Both from the figure and from 

 the photo it wiU be seen that here, curiously enough, the fungus lies 

 internally to the epidermal cells. There is no special apical cell or group 

 of cells, the whole apical region of the prothallus being meristematic. The 

 succession of five swollen fungal regions shows very clearly that it is the 

 fungus which causes the swelling in the tissue of the prothallus, and that, 

 at any rate in this prothallus, the primary tubercle is in no wise different 

 from any of the later-formed tubercles. 



The prothallus shown in fig. 51 illustrates some interesting points in 

 comparison with that just described. There are six distinct fungal areas, 

 and the four lowest are closely approximated and are scarcely, if at all, 

 swollen. There is a well-developed filament at the base of the prothallus, 

 and the prothallus as a whole increases quite gradually in girth from this 

 upwards. Even the first-formed fungal region is practically unswollen. 

 I should judge that the extension in length of the prothallus in these 

 early stages had been comparatively rapid, there being no cessation in 

 growth in length consequent on the formation of a first generative region 

 or of the storing of food material. This state of things can bear close com- 

 parison with what takes place normally in the cylindrical much-elongated 

 epiphytic prothalli, in which growth is continuous and rapid and there is 

 an entire absence of swellings in the fungal regions. The adoption, or 

 rather, the preservation, of the definite apical meristem in the epiphytic 

 type is probably only the result of this habit of growth. The prothallus 



