IX 



iWA/^A rriACE/E—ISOETA CE^ 283 



nucleus contains a lar<;e round body (nucleolus ?) that stains 

 very intensely, but otherwise shows little chromatin. The 

 receptive spot is of unusual size, and occupies about one-third 

 of the egg. It is almost hyaline, showing, however, a faint 

 reticulate arrangement of fine granules ; the lower portion of 

 the Qg^ is filled with granules that stain strongly. 



In /. /aaistris, according to Hofmeister,^ only one arche- 

 gonium is formed at first, and if this is fertilised, no others are 

 produced ; but in /. echuiospora, even before the first archegonium 

 is complete, two others begin to develop and reach maturity 

 shortly after the first, whether the latter is fertilised or not. 

 In case all of these primary archegonia prove abortive, a small 

 number, apparently not more than five or six, may be formed 

 subsequently ; but so far as my observations go, the production 

 of archegonia is limited, as is the growth of the prothallium 

 itself." 



The development of the prothallium goes on without any 

 increase in size, until the first archegonium is nearly complete, 

 about which time the spore opens along the line of the three 

 ventral ridges, and the upper part of the enclosed prothallium 

 is exposed, but projects but little beyond the opening. In 

 case all the archegonia prove abortive, the prothallium con- 

 tinues to grow until the reserve food material is used up, but 

 then dies, as no chlorophyll is developed in its cells, and only 

 in very rare instances are root-hairs formed. 



The Embryo 



Besides the earlier account of Hofmeister,^ Kienitz-Gerloff'* 

 and Farmer ^ have made some investigations upon the embryo- 

 geny of /. lacustris, which correspond closely, so far as they go, 

 with my own on /. ecJiinospora. 



The youngest embryos seen had the first division wall 

 complete (Fig. 148, D). This is transverse, but more or less 

 inclined to the axis of the archegonium. The nuclei of the 

 two cells are large and contain several chromatin masses. The 

 second division in the epibasal and hypobasal cells does not 



^ Hofmeister (i), p. 340. 



■' Kienitz-Gerloff (6) states that in old prothallia of /. laciish-is the number is 

 sometimes twenty to thirty. 



^ Hofmeister ( I ). * Kienitz-Gerloff (6). ^ Farmer (2). 



