408 



Mr. W. H. Lang. On the Prothalli of 



The youngest prothallus obtained was a short cylindrical body a little 

 over one-sixteenth of an inch in length. The lower end was darker in 

 tint and bore a number of short rhizoids, while above this, where the 

 antheridia were situated, the surface was of a lighter colour. The 

 apex itself was bluntly conical and almost white. In slightly larger 

 prothalli the contrast between these two regions was more strongly 

 marked. The lower, vegetative region increases in size and becomes 

 lobed, while the antheridia are confined to the cylindrical upper 

 portion, which continues to increase in length. This latter region 

 appears to be longer and the lobed basal part relatively less developed 

 in prothalli which bear the antheridia (fig. 2). Seven of the young 

 prothalli found were male ; the other two bore archegonia only. 

 These female prothalli were stouter and more lobed than the male 

 ones, and the ^diameter of the short apical region, on the surface of 

 which the archegonia were situated, was almost the same as that of 

 the vegetative region. There thus appears to be a partial sexual 

 differentiation in the prothalli of HeJmintJiost('.c]u/s, but both antheridia 

 and archegonia may occur on the same prothallus, as some of the latter 

 attached to young plants have shown. The antheridia are large and 

 often closely crowded together. They hardly project from the 

 surface, the wall being only slightly convex. The archegonial neck, 

 which is formed of four rows of cells, projects distinctly from the 

 prothallus. 



The distinction made above between a vegetative and a reproductive 

 region in this prothallus is supported by the distribution of the 

 endophytic fungus. This is entirely absent from the reproductive 

 region, but in the basal part occupies a wide zone between the two 

 or three superficial layers of cells and the central tissue, which are free 

 from the fungus. 



The young plants attain a considerable size while still attached to 

 the prothallus. Plants with three leaves and as many roots have 

 been seen, the prothallus of which showed no sign of decay. The 

 first leaf is ternate and has a leaf-stalk of variable length. The 

 lamina is green and reaches the light, A single root corresponds to 

 each of the early leaves. 



Examination of the prothalli connected with young plants indicates 

 the position they occupied in the soil. Most commonly the long axis 

 of the prothallus was vertical ; sometimes, however, it was oblique, 

 and occasionally horizontal. 



Psilotum, sp. 



The prothallus of this plant was looked for without success in 

 Ceylon, both in the mountain region and on the roots at the base of 

 Cocos palms near the coast. In the localities visited on the west coast 

 of the Malay Peninsula Psiloium was not abundant. On Maxwell's 



