Two Fossil Prothalli. 31 7 
his second specimen only a matured archegonium and a few 
adjacent cells are preserved, but the specimen is of great interest. 
The neck of the archegonium, consisting of three rows of cells, 
also the internal cells, are excellently displayed. 
Lepidostrobus Veltheimianns seems, therefore, to have been of 
a type more reduced than the present example, as the archegonial 
layer of tissue is developed only in the mouth of the spore, not 
extruded from it as in the present instance, and also because the 
neck of the archegonium is reduced in length. 
Renault 1 has also described imperfectly preserved prothalli from 
undetermined megaspores of Lepidostrobus , and the fine prothallus 
recorded by Dr. Margaret Benson in the megaspore of Mazocarpou 
is well known. 3 The large irregular masses of “ cells ” sometimes 
found inside megaspore walls, and labelled “ prothalli ” are 
more probably merely mucilaginous vesicles formed by the break¬ 
down of the previously-contained reserve material. 
The uncommon position of the prothallus here described, 
A 
B C 
Text-Fig. 2. 
A. Lepidostrobus veltheimianus : prothallus. After Mrs. D. H. Scott. x20. 
B. Mazocarpou : immature prothallus. After Dr. Margaret Benson. x24. 
C. Salvinla natans : embryo in prothallus, which is situated in the open 
mouth of the spore. After Pringsheim. x66. 
D. Selaginella : mature prothallus, with beginning of segmentation of food 
material within spore. V=vacuole. x66. 
1 See Lotsy. “ Botanische Stammesgeschichte,” II. p. 458. 
2 See Scott. “ Studies in Fossil Botany.’’ 2nd Edition, Part I, 
p. 189. Also Benson, “ The Sporangiophore*” New Phyt., 
Vol. VII, Nos. 6 and 7, 1908. 
