Hollowat. — Prothallus, &c, of Tmesipteris. 405 



Not infrequently two apical cells, one in each epibasal quadrant, are set 

 apart more or less simultaneously at an early stage. The youngest embryo 

 which showed this feature is that in fig. 48, the apicals lying alongside one 

 another at the apex of the shoot, separated only by the quadrant wall. 

 Three other embryos, at rather older stages of development, which possess 

 two apicals. are shown in figs. 55a and 55b, 56a and 56b ; and 57a and 57b. 

 While at first segments are cut off from the apicals rather towards the base 

 of the embryo than outwards, all-round segmentation soon begins, and they 

 become more widely separated, inclining from one another, as in the 

 figures, at an obtuse angle, or even eventually in exactly opposite directions. 

 In the Tmesipteris embryo the apical cells are always large and are readily 

 observed, the regular arrangement of cells cut off from them being also a 

 distinguishable feature. The growth of the young shoot from two similar 

 apices will be dealt with in the next section of this paper, but the fact that 

 the two apices are sometimes present together in the young embryo is 

 noteworthy. 



When only one shoot-apex is present a certain amount of cell-division 

 takes place in the other quadrant until the young apex has actually burst 

 through the prothallial tissue. The second quadrant thus forms a smooth 

 rounded base to the shoot proper, consisting eventually of a uniform tissue 

 of large-sized cells in which the symbiotic fungal coils early establish them- 

 selves. Before it emerges from the surface of the prothallus the shoot is 

 more or less globular in shape, but the apex or apices soon become beak- 

 like in form (Plate LXIII, fig. 2. and fig. 58a). A strand of elongated and 

 narrow conducting-elements is early differentiated at the centre of the 

 epibasal region by the longitudinal division of the cells there situated 

 (figs. 56a, 56b, 57a, 57b). As the apex grows forward these narrow elements 

 curve round and lead up behind it, extending back almost to the main basal 

 wall. When there are two apices present the two strands both lead down 

 in this way towards the foot. The haustorial protuberances early arise all 

 over the foot-surface by the outward growth of its superficial cells, and the 

 foot as a whole sometimes assumes a very irregular shape (figs. 54, 56a, 

 56b, 57a, 57b). The full development of these outgrowths is not attained 

 until the young plantlet has become well advanced. Starch is often present 

 in the foot and central cells of the embryo in large quantities, and in the 

 cells of the prothallus also which lie adjacent to the foot (figs. 56a, 56b). 

 On account of the rapid cell-divisions, and also of the large size of the 

 nuclei in the upper region of the young embryo, mitotic figures can often 

 be seen here to great advantage. 



The Young Sporophyte. 



A. The Rhizome. 



The forward growth of the young plantlet after it has emerged from 

 the prothallial tissues is illustrated in figs. 58a, 59a, and 59b. In the 

 former of these there is only one apex, and on account of its lower part 

 not being cut medianly the conducting-strand does not appear. In the 

 latter there are two equally-developed apices of growth, each with its 

 conducting-strand. This plantlet had become detached from its prothallus. 

 It may be compared with that shown in fig. 65 in my previous paper. 

 Although for a considerable time the young plant is dependent upon its- 

 parent prothallus for the main food-supply, as evidenced by the continued 

 extension of the haustorial outgrowths of the foot and the presence of 



