i 5 6 



ARCHEGONIATES. 



THE ARCHEGONIUM. 



The development of the archegonium in the Cycadacece and in 

 Ginkgo, which is similar to that of Pinus, is too well known to require 

 a detailed description in this place. The manner, however, in which 

 the large central cell is nourished during its growth by the immediately 

 surrounding cells of the prothallium is, if Ikeno's observations be cor- 

 rect, a phenomenon of a rather rare occurrence in the Gymnosperms, 

 and merits some special mention. These surrounding cells, which are 

 separated from the central cell by thick cellulose walls, are of a uniform 

 size, each possessing dense cytoplasm and a large nucleus. Before 

 the archegonium is full grown the nuclei of these cells show a fine and 

 distinct threadwork; but, as this organ approaches maturity, the 

 nuclei, with the exception of the nucleoli, are transformed into homo- 



cm. 



B 



FIG. 64. Three cells from layer of prothallial cells immediately surrounding upper part of central cell 

 of archegonium of Cycas, showing protoplasmic connections between these cells ; in B the beak of 

 nucleus extends into plasmic bridge. (After Ikeno.) 



geneous and diffusely staining bodies. This phenomenon is not confined 

 solely to the cells forming the wall of the archegonium, but it may 

 extend to adjacent cells of the prothallium. This nuclear change takes 

 place only in cells near the upper part of the central cell. 



Goroschankin has shown that in the Cycadacece fine cytoplasmic 

 connections exist between the central cell of the archegonium and the 

 surrounding cells. From Ikeno's figures it seems that the cytoplasmic 

 strands in Cycas are relatively large, and that large granular plasmic 

 masses pass over bodily into the central cell (Fig. 64, A, B). Fre- 

 quently the nucleus itself will send out a beak or protuberance toward 

 the nearest plasmic connection. Arnold! (1900) finds that in several 

 species of Pinus and in Abies the nuclei from the surrounding cells 

 pass into the egg-cell. The prevalence of condensed nuclei in cells 

 surrounding the upper part of the central cell is explained by Ikeno as 



