Thom — Fertilization in Aspidium and Adiantum. 287 



G, cleared with oil of cloves and mounted in balsam. In my 

 later studies on antheridia, I have fixed whole prothallia by 

 exposure to the fumes of osmic acid. The antheridia were 

 then dissected out with needles under a lens and stained 

 with Haidenhain's iron alum-haematoxylin and mounted in 

 glycerine. The spermatogenous cells could then be easily 

 crushed out. This method, however, gave no better results 

 than the study of antheridia in the sections prepared by the 

 former method, but as a check upon the earlier work the sub- 

 stantial agreement between results was of considerable value, 

 study and drawing have been done with a Leitz -^^2 oil im- 

 mersion, with a Nachet -^f oil immersion and latterly with 

 the. Zeiss Apochromatic 3.00 mm. apert. 1.30, using the Zeiss 

 No. 12 compensation ocular and the new Bausch & Lomb 

 camera lucida — giving a magnification of 1700 diameters. 



General Descriptive Notes. 



A description of the general morphology of the archegonium 

 and antheridium in the group would be superfluous. A few 

 observations upon the special distribution of organs on pro- 

 thallia may be of value. Prothallia bearing antheridia only 

 were often found in both forms, but such prothallia rarely 

 showed that typical heart-shape which is universally described 

 for this group of ferns. Their outline was usually irregular, 

 rarely showing the notched apex at all. In ordinary monoe- 

 cious forms antheridia are developed much earlier than arche- 

 gonia, and are freely distributed over about one-third of the 

 surface. This area extends from the base of the notch back- 

 ward. Antheridia are rarely found farther forward than the 

 base of the notch or closer to the edge than one-third of the 

 diameter of the prothallium. I have only once observed an 

 antheridium developed upon the upper surface. Neither 

 antheridia nor archegonia depart from the well-known de- 

 scriptions in general structure or development. The arche- 

 gonia in these forms are distributed only on a comparatively 

 small space ranging directly backward from the notch. On 

 older prothallia, if no embryo is developed, the area devoted to 

 the development of archegonia becomes sometimes quite large, 

 so that often a considerable number become ripe at once. In 



