Edgeklky. — Prothallia of Three New Zealand Lycopods 



97 



tissue from which the antheridia and archegonia arise on the upper surface 

 of the prothallium. 



In comparing the structure of this prothallium with that of L. clavatum 

 and of L. annotinum one or two striking differences appear. First is the 

 absence of a single layer of cells, elongated at right angles to the surface 

 of the prothallium, lying between the layers marked (b) and (c), in L. volubile, 

 and with the fungus intracellular. This layer of cells is represented by 

 Bruchmann as extremely well marked in L. annotinum, and by Lang as 

 quite distinct in L. clavatum. Secondly, the occurrence of the fungus in the 

 cell-cavities as well as in the walls of layer (c). 'Thirdly, the absence of 

 starch from layer (c) and its abundance in the cells of layer (d). 



Meristematic Tissue. 



The formation of new tissue takes place all round the margin of the 

 prothallium, just beneath the reproductive ridge. The meristematic cells 

 are found on the lower surface of a bay or indentation just below the re- 

 productive ridge (fig. 4, x). A section through this region shows a row of 

 cells with large deeply staining nuclei. These cells divide both by peri- 

 clinal and anticlinal walls. Towards the outer surface of the prothallium, 

 cells formed by anticlinal divisions gradually pass into the elongated cells 

 of the limiting layer ; while, within this, meristematic cells pass gradually 

 into the layers which contain the fungus hyphae. More internally, a layer 

 of secondary meristem seems to be differentiated, which gives rise towards 

 the upper surface of the prothallium to radial rows of small cells, and 

 below gradually passes into the large-celled parenchymatous storage region. 



Fungus. 



Mention has already been made of the fact that certain cells of the 

 prothallium harbour an endophyte. Not only does this fungus not injure 

 the prothallium, but no mature prothallium is found without it. More- 

 over, the cells in which the fungus is present are quite normal, and a 

 nucleus is always present in them, though it may be almost hidden in the 

 coils of the fungus. It seems quite clear that this is a case of symbiosis, 

 though the exact way in which the endophyte and the prothallium benefit 



7\H 



Fig. 5. — -Cells of L. volubile, containing skein of fungus hyphae. /./, fungal 



filaments. X 900. 

 Figs. 6, 7, 8. — -Cells of L. volubile, showing the formation of nucleated 



vesicles (nv). X 900. 



is not known. Possibly, in the first place the fungus attacked the pro- 

 thallium of Lycopodium parasitically, but the Lycopodium prothallium was 

 able to use the fungus to aid its nutrition. In any case, the fungus must 

 obtain some advantage from the association or it would not so generally 

 be found in the prothallial cells. Before the exact relation between the 

 two organisms can be determined it is necessary to know more about the 

 processes of nutrition in the fungus. 



4— Trans. 



