Hollowat. — Prothallus, &c, of Tmesipteris. 



411 



Adventitious branches are a well-known feature in older rhizomes of 

 Tmesipteris, where they sometimes apparently function as storage-tubers 

 before developing further. Laterally - developed adventitious apices may 

 be found also in quite young plantlets (figs. 74, 75, 81). One such was 

 present at the point indicated on the plantlet shown in longitudinal section 

 in fig. 65d. It projected very slightly 

 above the surface of the main stem, 

 and is shown in transverse section in 

 figs. 65a, 65b, and 65c, which represent 

 the first, second, and fifth sections 

 passing through it. A slight strand 

 of narrow elements led from behind 

 it to join the strand of the main 

 shoot. Another young adventitious 

 apex occurring in a similar position 

 is shown in figs. 66a and 66b. In 

 the section marked B the apex and 

 strand of the main shoot is cut longi- 

 tudinally, but the adventitious apex 

 and its strand does not lie quite in 

 the same plane. The apical cell of 

 the latter appears in the seventh sec- 

 tion from B, and is shown cut obliquely 

 at A. In figs. 67a and 67b a very 

 young lateral apex is shown cut trans- 

 versely. The section marked A passes 

 through the apical cell. This has 

 evidently been functioning for some 

 time, judging by the arrangement of 

 the cells in B, which lies six sections 

 below A. Deeper down towards the 

 main strand, however, the adventitious 

 strand has the appearance, as seen in 



C, as if it had arisen not from the apical cell, but by the subdivision of an 

 ordinary cortical cell of the main shoot. Sometimes a plantlet will show 

 a third apex of growth at its base in close proximity to the second apex, 

 as illustrated in longitudinal section in fig. 68. Here the main strand has 

 been cut obliquely transverse, since the foot into which it leads lies in a 

 plane at right angles to the direction of growth of the two young apices. 

 The latter also are not cut medianly throughout their length, so that the 

 course of their strands is not included in the figure. A plantlet in a similar 

 condition is also shown in general view at fig. 79. One very young plantlet 

 (figs. 69a, 69b, G9c) was found on sectioning to have three apices. Two 

 of these — namely, B and C — had given rise to well-defined strands, and had 

 probably been initiated in the embryo. The third, shown at A, had given 

 rise as yet to no strand, and lay rather out of the plane of the other two, 

 as can be seen from the fact that this section does not include the foot. 

 It must probably be interpreted as an adventitiously-formed apex rather 

 than as one which had arisen in the embryo. 



The apical cell of the main shoot in the young subterranean plantlet, 

 and its manner of segmentation, is shown in longitudinal section at fig. 71. 

 A series of transverse sections taken at intervals from apex to foot through 

 a young plant of about the same age as that shown at Plate LXIII, fig. 3. 



Fig. 68. — A young prothallial plantlet 

 in longitudinal section, showing the 

 primary apex and also two apices at 

 the base of the plantlet. X 45. 



