‘EMBRYOLOGY 347 
substantially the same: the hypocotyl becomes elongated as the seedling 
develops, and the whole appearance of the seedling resembles that of 
L. Selago. The primary segmentation in Z. Phlegmaria is according to 
the scheme (Fig. 182), and the lower tier, as in Z. Se/ago, forms only the 
foot, which attains no great size (Fig. 185). The upper tier develops 
unsymmetrically from the first, the side which will form the first leaf 
growing more strongly; close to the base of the cotyledon, and apparently 
lateral owing to the stronger growth of the latter, but in reality terminal, 
arises the apex of the axis (T, Figs. 185 a, B); it is, in fact, initiated in 
close proximity to the organic centre of the upper tier. The root 
(R, Fig. 185 8) also originates from 
the upper tier. A comparison of 
Treub’s drawings of Z. Phlegmaria 
with Bruchmann’s less complete 
series for Z. Se/ago shows clearly the 
substantial similarity of the embryo- 
geny in the two species. It will 
be remembered that the flattened 
prothalli of the latter species, formed 
near the level of the soil, have been 
held to prefigure the strap-shaped 
sexual branches of the Phlegmaria 
prothallus, though the latter shows 
its higher specialisation for a sa- 
prophytic habit in its filamentous 
development and in its frequent 
branching. On the other hand, as 
regards the sporophyte, it has been 
seen that the Phéegmarza type is not 
one of the highest developed, but is Prothalll of Lyratodines Selaze with seedling plants. 
associated with Se/ago in the sub- 
genus Uyrostachya. This being so, it is natural to find their embryos so 
similar, notwithstanding the difference in specialisation of the prothalli 
themselves. Lastly, both embryos are from the first subaerial: their first 
leaves are green assimilating organs, and differ in no essential degree from 
the normal foliage leaves. This may probably be held to be a primitive 
condition. 
But in the clavatum-annotinum-type the case is different. It has been 
seen that there the prothallus is developed underground, often at a considerable 
depth, and this brings with it modifications of the embryogeny. The first 
steps in the development are the same as in the types described above 
(Fig. 1864); but very soon there is a conspicuous enlargement of the 
tissue of the foot, derived from the lower tier, adjoining the suspensor 
(Fig. 1868): a large spherical swelling is thus formed, which remains as 
an intra-prothallial haustorium (compare Fig. 1798 with Fig. 186c). The 
Fic. 184. 
