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Transactions. 



Older prothallia — e.g., that represented in fig. 3 — seemed to form a 

 rather flat plate, with a ridge running round the margin of the upper 

 surface. This flattened form was particularly noticeable in some of the 

 prothallia to which young sporophytes were attached. 



Internal Structure. 



The internal structure of the prothallium of L. volubile agrees in its main 

 characters with that of L. clavatum or L. annotinum. A glance at fig. 4 

 shows that there is a differentiation into several layers of tissues which 

 correspond in a general way to those of L. clavatum. The following tissues 

 can be distinguished : — 



(a.) On the lower surface a limiting layer of cells, elongated parallel 

 to the surface and destitute of fungus hyphae, except certain cells which 

 form the basal cells of rhizoids. 

 These rhizoids apparently have no 

 fungus hyphae in their cavities, 

 the hyphae penetrating the wall 

 of the basal cell and ramifying in 

 the humus. 



(h.) Next come several layers 

 of equi - dimensional cells, thin- 

 walled, whose cavities are densely 

 packed with fungus hyphae, which 

 stain deeply with haemalum. 

 Nuclei are present in these cells, 

 but are often somewhat obscured 

 by the fungus. Those cells which 

 border on layer (a) are often less 

 densely filled with fungus. 



(c.) Then follows a rather wide 

 band of nucleated cells, elongated 

 at right angles to the surface of 

 the prothallium. The cell-walls 

 are thick, and many of them con- 

 tain fungus hyphae. which collect 

 especially where two or more cell- 

 walls meet. The presence of the 

 fungus filaments in the walls 

 renders it rather difficult to see 

 the exact shape of the cells. This 

 layer also has the fungus in the 

 cell-cavities. 



The layers marked (b) and (c) extend not only parallel to the base but 

 also parallel to the sides in the younger radial prothallia. In the older, 

 more flattened, forms only a few rows of cells immediately below the re- 

 productive organs are free from the fungus. From the layer (c) starch 

 is absent. 



(rf.) The whole of the central part of the prothallium is occupied by 

 large thin-walled parenchymatous storage-cells, in which starch is stored 

 in great abundance. The cells of this tissue bordering on (c) are often 

 smaller and more densely filled with starch granules. 



(e.) The layer (d) passes gradually into a rather delicate layer of small- 

 celled tissue, which passes into more or less radial rows of small-celled 



Fig. -4. — Section of young prothallium of L. 

 volubile. a, limiting layer ; b, cells with 

 intercellular fungus : c, cells with inter- 

 and intra -cellular fungus ; d, storage 

 tissue; e., generative tissue ; rh, rhizoid. 

 X 82. 



