Two Fossil Prothalli. 
309 
limiting layer of small cells which are roughly square in shape. To 
this succeeds, centripetally, a wide band of tissue composed of 
elements radially elongated, while the central portion is occupied 
by a mass of rounded cells. Unfortunately, these last do not show 
very plainly in the figure, because, although they are clearer in 
the original, a large quantity of granular dirt obscures the arrange, 
ment. This sort of appearance in transverse section is decidedly 
reminiscent of the prothalli of recent Gymnosperms. 
The method of formation of alveoli in the Gymnospermous 
prothallus was first described by Hofmeister 1 in Pinus. He fell 
B 
Text-Fig. 1. 
A. Pinus sylvestris. Part of the longitudinal section of the prothallus. 
X 106. 
B. Pinus sylvestris. Upper end of the prothallus, showing the peripheral 
layer, x 160. 
C. Ephedra vulgaris. Upper portion of the prothellus. x 160. 
D. D'. Dioon edule. Transverse sections of the prothallus. D is slightly 
younger than D'. x60. 
A, B and C after Mile. Solokowa. D, D' after Chamberlain. 
into the error of supposing that the first endosperm, formed in 
summer, was a cellular structure developed by ordinary cell-division, 
’Hofmeister. “ Vergleichende Untersuchungen.” Pp. 141, 127, 
129. 
