ATKLXSON: THE GENUS ENDOGONE 7 



homogeneous as in the gametangia. But as the new zygote enlarges 

 the cytoplasm becomes coarsely reticulate. The strands are coarse 

 and with an irregular outline. They radiate irregularly from the 

 center to the periphery and anastomose by irregular branches, forming 

 a large meshed network the strands of which are coarser in the central 

 region, thinner toward the periphery. During the early stages of 

 development of the young zygote the nuclei appear to have a general 

 distribution, but have not been observed near the periphery. As the 

 zygote approaches its full size the nuclei occupy the more central 

 region, being distributed from the center to a zone half way, or a 

 little more, to the periphery. Sometimes the centralization is more 

 marked. At this stage there appears to be a differentiation of the 

 cytoplasm, or rather, the appearance of a clear homogeneous plasma 

 occupying the nuclear region and in which the nuclei die. When the 

 nuclei are strongly centralized, the homogeneous plasma appears to 

 form a single large central area. When they are more widely dis- 

 tributed, the homogeneous plasma is separated into several areas, 

 each area containing several nuclei. During all this period the coarsely 

 reticulate cytoplasm occupies the entire zygote. 



A provisional suggestion as to the function of this homogeneous 

 plasma is that it serves as a medium for the freer movement of the 

 nuclei than can take place in the coarsely reticulated cytoplasm; or 

 the homogeneous plasma may actually serve to move the nuclei to a 

 certain extent, possibly bringing them into closer proximity in the 

 center and later carrying them into the peripheral zone. In this 

 central region the nuclei are generally in pairs and the two nuclei of a 

 pair appear to fuse. This fusion of paired nuclei in the zygote corre- 

 sponds with the fusion of paired nuclei in certain of the Mucorales as 

 described by Gruber (1901) in Sporodinia grandis, Dangeard (1906) in 

 Rhizopus nigricans, and Moreau (1911-1913) in Rhizopus nigricans 

 and species of Zygorhynciis. The fusion of the nuclei of a pair is 

 suggested by the fact that they are found close together, sometimes 

 the nuclear membranes in contact, again an elongated nucleus (? 

 fusion) with one membrane and this constricted between the two 

 nucleoli, and further two nucleoli surrounded by one membrane which 

 is not constricted. Of course these relations might be the result of 

 nuclear division, but no figures appear at this stage which suggest a 

 division of the nuclei. 



In a later stage of development the coarse reticulum of the cyto- 

 plasm disappears. The cytoplasm becomes more homogeneous. 

 The nuclei appear to occupy a zone about half way between the 

 center and periphery. Figures are present which suggest a division 

 of the nuclei at this stage, for the nuclei are often two to three times 



