388 Transactions. 



invariably to be found on tree-fern stems, but with the different advantage 

 that the humus lacks the irritating entanglement of tough aerial tree-fern 

 rootlets and is easily crumbled down. I have found that Tmesipteris occurs 

 in this station more particularly at middle altitudes in the district, on the 

 lower parts of the mountain-flanks and in the valleys, where the rainfall 

 is even heavier than at the sea-coast ; and, although I have not often found 

 large colonies of the young plants in these situations, I feel sure that a 

 systematic investigation of these large overhanging tree-trunks would show 

 that the plantlets occur not infrequently. From one particular rata in the 

 valley of the Greenstone River, on the lower parts of the Hohonu Range, 

 at an altitude of about 1,300 ft., I took home on each of three occasions a 

 parcel of humus and secured altogether no less than 580 prothalli. 



On the flanks of the ranges Tmesipteris is frequently to be met with 

 growing in the thick humus on the forest-floor either as single plants or in 

 colonies, although here, owing to the dense accumulation of undecayed 

 vegetable debris, germination of the spores probably does not take place 

 frequently. 



The Prothallus. 



I have already given (7) a fairly complete account of the form and 

 structure of the prothallus and development of the sexual organs. As a 

 result, however, of the study of the very large number of prothalli since 

 discovered by me there are some additional facts to be noted. 



Of the total number of prothalli found on the one rata, as mentioned 

 in the previous section of this paper, about one hundred were quite young — 

 that is, they were from 1 mm. to 2 mm. in length. A good many of these 

 showed the original spore still attached. The youngest found was just 

 under 1mm. in length, and is shown in general view in fig. 1. It had 

 developed no sexual organs. Its lower two-thirds was brown in colour, 

 as also were the rhizoids, but the head was colourless. Throughout the 

 brown region the cell-walls showed very distinctly, as is always the case 

 in the Tmesipteris prothallus, while the cells themselves each contained a 

 circular compact fungal skein. At the uppermost limit of the brown 

 region, however, the fungal skeins were thin and delicate. The browning 

 of the cell-walls extended slightly beyond the point reached by the fungus, 

 and also a slight general tinge was beginning to show on the left side of 

 the head. This brown or almost golden-yellow colour is characteristic of 

 both young and old prothalli of Tmesipteris, except for the actual head, 

 and it seems to arise very early in the development. Darnell-Smith 

 (3, p. 86) notes that in Psilotum the first cells formed on germination of 

 the spore are light brown in colour, and that the fungus begins to infect 

 the prothallus at the three-cell stage. He also notes (ibid., p. 88) that the 

 small bulbils borne on the older prothalli are colourless in the early stages 

 of growth, but later become brown. The cells of the head of the prothallus 

 shown in fig. 1 were large and bulging, and contained much starch. There 

 was no basal filament of a single cell in thickness, as is sometimes to be 

 seen even in older prothalli (7, figs. 1, 11), but the prothallus began 

 immediately from the spore to increase gradually in width by cell- 

 multiplication. The fungus was present in the lowest cells of the 

 prothallus and in the spore also. The basal region of another young 

 prothallus with the spore attached is shown in fig. 2. The wall of the 

 spore is thick, and its outer surface pimpled. 



Older prothalli not infrequently show the basal end intact, and in some 

 cases the spore can still be seen attached. Fig. 4 shows in general view 



