Holloway. — Prothallus, &c, of Tmesipteris. 415 



in longitudinal section, in which that part of the epibasal region contained 

 within the prothallial tissues was of unusual length. The extra-prothallial 

 shoot-region is cut somewhat obliquely, so that the course of the strand 

 becomes lost. 



From the above account it will be seen that the young sporophyte of 

 Tmesipteris, before the development of the aerial shoot, shows variations in 

 form. A number are given in figs. 73 to 87, and with these can be 

 compared others illustrated in my previous paper at figs. 66 to 72. The 

 development of a third apex of growth has given an irregular form to those 

 shown at figs. 80, 85, 86, and 87. In the plantlet at fig. 82 probably the 

 longer of the two branches was the one secondarily developed, and it here 

 occupies an unusual position. Some of these figures show that the plantlet 

 may attain a considerable size while still attached to its prothallus. When 

 detached they generally show a fragment of old prothallial tissue still 

 attached to the foot, frequently in the form of a dark ring. The plantlet 

 apparently becomes detached from the prothallus at the basal wall, and 

 sections through a prothallus at an old point of attachment invariably 

 show the whole foot of the plant still embedded in its tissues. 



It may be stated here that throughout the life of the sporophyte no 

 indications are to be met with of the adoption of any special root-like 

 function on the part of any of the branches of the rhizome. These 

 branches are all similar to one another in both external appearance and 

 internal structure. 



B. The Aerial Shoot. 



The young wholly-subterranean plantlet frequently attains a length of 

 Jin. to fin. before forming an aerial branch. Generally one of the two 

 main growing apices turns up out of the soil, the other continuing to extend 

 in the humus (figs. 88, 89). In some cases both ends may grow out into 

 aerial shoots (fig. 90, and 7, fig. 73), the rhizome-system then extending by 

 the formation of lateral branches. Again, in other instances, the first aerial 

 branch arises laterally, the main apices of the rhizome continuing under- 

 ground (7, fig. 5). 



The aerial shoot is much thinner than the rhizome, and is at first quite 

 scaleless and leafless. Usually when the shoot is from \ in. to \ in. high, 

 leafy outgrowths are formed immediately behind the apex, but these form 

 only scale leaves. The first aerial shoot generally does not grow more than 

 1 in. or 2 in. in height, and remains very slender and sterile, withering off 

 when other shoots are formed. Frequently the second may do the same ; 

 but those next formed are much longer, although still slender. The mature 

 well-grown shoots are to be found only when the rhizome-system has 

 become strongly developed. In most cases aerial shoots remain unbranched, 

 but a single forking sometimes takes place at or near the base, or occasion- 

 ally, in well-grown pendulous branches, even higher up. 



At the base of well-grown aerial shoots there is generallv onlv a short 

 region bearing the scattered scale leaves, the ordinary form of the leaf being 

 fairly early and often suddenly attained, but the first shoots of the young 

 plant frequently show a much longer scale-leaf region. In the latter tha 

 transition to the larger form may be either sudden or gradual. There is 

 much variation in the size shown by the mature sterile leaf, this generally 

 being longer, as might be expected, in pendulous branches than in those of 

 more erect growth. The leaves of juvenile plants, also, are rather small 

 in size. Sometimes however, elongated pendulous branches show a much 



