Holloway. — The Prothallus and Young Plant of Tmesipteris. 27 



ment of the young plant, in these cases the plantlets having become 

 detached from their parent prothalli during the process f dissection. 

 I have no plantlets of this age in section, but judging from its conical and 

 somewhat pointed shape I would say that the actual apex is occupied by 

 a single apical cell. That end of the young plant which is opposite to the 

 growing apex is obviously the " foot " or absorbing region, where the 

 plant was in connection with the prothallus. In the detached plantlets 

 shown in figs. 64 and 65 this end is roundish in outline, it being evident 

 that the haustoria-like processes of the foot had been left embedded in 

 the tissues of the prothallus. Still older plantlets consist of a lengthen- 

 ing undifferentiated rhizome, golden-brown in colour, thickly clothed with 

 long straight golden-brown rhizoids. Where the rhizoids are broken off, 

 characteristic ring-like outgrowths are left projecting slightly from the 

 epidermal cells. The latter are brown in colour, and, owing to the clear 

 colour of the rhizome generally, stand out very distinctly in outline. 

 The original point of attachment of a detached plantlet of this age to its 

 parent prothallus can always be readily distinguished as a dark circular 

 patch situated on a slight but distinct conical prominence at the basal 

 end of the rhizome. Sometimes there is a brown fragment of prothallial 

 tissue which may show old sexual organs still attached to this foot- 

 prominence. 



The manner of detachment of the plant from its prothallus may best 

 here be described. It was found during the process of dissecting that 

 the plantlets very easily become detached from their parent prothalli. 

 Reference to the longitudinal section of the plantlet and prothallus 

 given in fig. 59 will show that a saucer or cup-shaped line of dehiscence 

 extends from the edge, where the developing plant has ruptured the tissues 

 of the prothallus, down into the central regions of the foot. This line 

 of dehiscence is clearly marked out by the browning of the cell-walls 

 along the line. Figs. 58 and 59 show clearly both how readily the plant 

 can become detached from the prothallus, leaving behind in the tissues 

 of the latter the haustoria-like processes, and also how the large cup-like 

 point of attachment, which so often is a characteristic feature on full- 

 grown prothalli, comes to be formed. 



All the youngest plantlets found, whether detached or still in connection 

 with the prothallus, showed only one apex of growth, the other end of the 

 plantlet being bluntly rounded and in no way differing in external appear- 

 ance from the rest of the rhizome surface (figs. 66 and 67). The point of 

 attachment to the prothallus was at this undifferentiated end of the plant. 

 Longitudinal sections of the prothallus and plant shown in fig. 66 revealed 

 that there was nothing at this end of the plant to indicate an apex of 

 growth. Sooner or later, however, a new apex of growth is differentiated 

 at this point (figs. 1, 68, 69), and the young rhizome then proceeds 

 to grow in length in a direction more or less exactly opposite to 

 the primary direction of growth. This new portion of the plant- 

 rhizome is sometimes in a straight line with the first-formed shoot 

 axis (fig. 70), but more often is inclined to it at an angle, the brown 

 point of attachment in the latter case being then to be seen on the 

 angle (figs. 65, 69, 71). In some instances this secondary apex of growth 

 was not differentiated until the plant had attained a considerable size 

 (figs. 67, 68, 69), but in others, again, it was differentiated early (fig. 65). 

 In fig. 1 is shown a plant attached to its prothallus in which the main 

 shoot had a very irregular and peculiar appearance, and at the base of 



