Anthocerotales. 345 
embedded in and continuous with the thalius tissue, instead of 
being entirely free on the surface. 
The oospore divides by longitudinal and transverse walls so as 
to form three tiers of four cells each, and in all probability these 
tiers give rise to the three regions of the mature sporophyte—the 
more or less bulbous foot, the meristem, and the capsule. The 
cells of the upper tier are next divided by walls which cut off four 
central cells from a layer of outer cells ; but now the course of 
development diverges from that typical of other Liverworts. In 
the latter, the central tissue (endothecium) becomes the sporo- 
genous tissue, but here it remains sterile and forms an actual rod 
or columella, while the archesporium is cut out of the peripheral 
layer and, moreover, is hemispherical, extending over the apex of 
the columella (this is the case with the fertile portion of the arche¬ 
sporium in Pellia). The original four rows of cells forming the 
columella increase to sixteen rows, the archesporium becomes 
two-layered, and the capsule-wall becomes about four cells deep, 
the outermost layer forming a sharply marked epidermis with 
cuticle and stomata. The cell-divisions in the meristem zone below 
the capsule correspond with those in the capsule region of the 
embryo, and owing to the active growth of this zone the capsule 
continues to elongate for a considerable time, additions being made 
to columella, archesporium, and wall. The archesporial cells 
become differentiated into large globular spore-mother-cells and 
variously shaped sterile cells which remain irregularly united to 
form a network. The cells forming the sporogonial wall are 
separated by air-spaces which communicate with the stomata in 
the epidermis, and each cell contains two chloroplasts. The stomata 
are quite like those of the Vascular Plants ; each is formed by 
splitting of a cell which has remained oval while the surrounding 
epidermal cells have become elongated. As the spores ripen, the cap¬ 
sule-wall splits, from the apex downwards, into two valves, between 
which the thread-like columella projects. The columella has a 
mechanical function in strengthening the long sporogonium and 
holding together the network of sterile cells with the spores in its 
irregular meshes, but its primary function is doubtless that of 
transporting water and salts, absorbed from the thalius by the foot, 
to the green assimilating tissue of the capsule-wall, by way of the 
sterile cells, as well as to the developing sporogenous tissue. The 
sterile cells when young contain abundant starch and proteids. The 
developing spores are therefore very efficiently supplied with food by 
