1902] GAMETOPHYTES AND EMBRYO OF PODOCARPUS 97 
surface. The outer layer, however, is of an entirely different 
character. . It is composed of very small, regular, epidermis-like 
cells with dense protoplasm, but almost free from the starch 
grains found abundantly in other parts. This layer is absent at 
the tip of the prothallium and is not quite so regular at the base. 
No such definite layer seems to have been described for other 
gymnosperms,* but in Taxus I have found the outer cells to 
approach these in character, though not so definitely arranged or 
so small proportionately. There is little doubt that these sur- 
face cells are specially modified for secretion, and it is worth 
noticing that when a spongy tissue is present there they are not 
found. 
The larger cells of the prothallium, as is usual in conifers, 
contain many nuclei at the time the embryos are formed (fig. 20), 
while those on the surface have generally only one, or sometimes 
two. 
- In only one case were two prothallia found in one ovule 
(fg. 79). Neither had formed archegonia, although the seed 
had reached its full size. In one of them three or four tracheids 
Were present (fig. 20). This will recall the formation of trach- 
eids in the prothallia of ferns in cases of apogamy. In no other 
case of which I am aware have tracheids been described in the 
-Prothallium or endosperms of higher plantes; 445. 235 
= Hofmeister (1851) found two prothallia in the ovuleof Zazus 
: Pinus silvestris (ein solcher steht an einer sumpfigen Stelle S 
_. “<ip2iger botanischen Garten), welche, ahnlich der Eybe, _ 
| ae Mehrzahl ihrer Eychen zwei Embryosacke entwickeln."5 __ 
cs 990) and Arnoldi (1899) have found it the rule fore 
; embryo sacs to be developed in Sequoia se EperURTERS, | 
___-\1900, 6) figures five in Cunninghamia, and I have once 
: vad ieee |Taxodium. The case of Gnetum is well known 
nn. (1898) figures smaller and denser surface cells in Cycas, but they do 
from the adjoining cells below as in Podocarpus. a 
ee Annals of Botany 6:213. 1892) is describing g two prothallia ° a ia in 
ee ‘this previous discovery by Hofmeister. 9 - 
