Hollo way. — Prothallus, &c, of Tmesipteris. 



417 



slender branches, but to be seen also in older ones. Again, they may be 

 arranged in three or in four orthostichies, the stem in transverse section 

 showing a corresponding number of ridges. These different leaf-arrange- 

 ments may be found intermixed along the one branch . The leaves are never 

 in whorls, but are scattered. 



In pendulous branches the sporophylls are grouped in zones alternat- 

 ing with sterile zones. A characteristic very short and compact variety 

 may sometimes be found on tree - ferns in which the whole of the 

 upper two-thirds of the branch is fertile, there being no zoning. The 

 two or three first-formed small aerial shoots in the young plant remain 

 sterile. Sporophylls generally make their first appearance singly, juvenile 

 shoots about 4 in. to 6 in. in height commonly showing one sporophyll 

 situated about half-way along their length, and sometimes also another 



35 



Fig. 92 — -Portion of sporophyll, showing abnormal number of loculi in the 



synangium. X 1*5. 

 Figs. 93a, 93b. — -A sterile leaf in side and face views, showing a lobe-like 



outgrowth from the lamina. X 3. 

 Fig. 94. — The upper portion of a sterile leaf showing a small marginal 



outgrowth and thickening. X 3. 

 Figs. 95a, 95b. — The apex of a sterile leaf in side and face views, showing 



forking of the tip. X 3. 



borne singly still nearer the apex. Well -grown shoots showing the usual 

 alternate fertile and sterile zones may be found with these single sporophylls 

 towards the base. Occasionally a juvenile shoot is found in which the 

 sporophyll formation has been initiated not singly but in a normal zone. 

 The lobes of the sporophyll are similar in form, and sometimes also almost 

 in size, to the sterile leaf appendages, but generally they are narrower. 



" Abnormalities in the sporophylls have been described by A. P. W. 

 Thomas (15). I have occasionally found synangia with three loculi instead 

 of two (fig. 92), and not infrequently it happens that one of the lobes of the 

 sporophyll is more or less reduced in size, or is even almost entirely absent. 

 A sterile leaf in one instance bore about half-way down its flat surface a small 

 lobular outgrowth (figs. 93a and 93b), the appearance being that of an abortive 

 forking. Both sterile leaves and the lobes of the sporophyll sometimes 

 show a slight projection at the margin with the tissues of the lamina 

 thickened immediately behind it (fig. 94), suggesting a less-developed stage 

 • 14— Trans. 



