38 L ang. — Prothalli of Ophioglossum pendulum 
since the amount of reserve material is different in different 
individual a corresponding variation in size is found. That 
size is no safe guide to the age of the prothallus a com- 
parison of Figs. 30 and 34, which represent prothalli on the 
eve of arrest of growth owing to the exhaustion of their 
reserve food, clearly shows. 
In the above account the nutrition of this prothallus has 
been regarded chiefly as shown in the male individuals. An 
equally full series of the female prothalli was not available, 
and in all examined the Fungus was in the shrivelled, dead 
condition described above. In prothalli such as those in Figs. 
36 and 37, in which the young plant is just becoming visible, 
nearly all the cells of the large, lobed, vegetative region are 
packed with starch-grains. The cessation of growth does not 
here depend on the exhaustion of the food material, but on 
the fertilization of an archegonium and the subsequent 
changes. Judging from a large number of female prothalli 
attached to young plants, fertilization usually occurs when 
only a short sexual region bearing archegonia has formed. 
The large amount of reserve material remaining is here 
available for the nourishment of the embryo and young plant ; 
its exhaustion is not complete, though nearly so, when the 
first leaf of the latter is expanded and exposed to the light. 
The position of the sexual organs has been indicated above. 
It remains to describe their structure and development. The 
antheridium is referable to a single superficial cell, the first 
division in which is periclinal, and separates the wall from the 
cell which forms the spermatozoids. Figs. 50-52 (PL III) 
are from median sections of developing antheridia, and Fig. 52 
should be compared with Fig. 53 a , b , which represent two 
horizontal sections through an antheridium of corresponding 
age. A certain regularity exists in the earlier divisions in 
both the outer and inner cells. The former is first divided 
into four by anticlinal walls ; the latter becomes divided by 
successive walls into octants and, by further divisions, is con- 
verted into the mass of small spermatocytes. 
The mature antheridium presents some peculiarities. Like 
