220 



BOTANY 



Cell-structure. All Anthocerotales agree in the structure of the thallus. 

 The apical growth is similar to that in the lower Jungermanniales, but a pecul- 

 iarity is the presence of a single chromato- 

 phore in each cell, which thus recalls that 

 of many Confervacese, like Coleochaete or 

 Chsetophora. Upon the lower side of the 

 thallus, which is attached to the substratum 

 by simple root-hairs, are stoma-like clefts, 

 which communicate with cavities filled with 

 mucilage. Through these mucilage-clefts 

 filaments of Nostoc enter the thallus and 

 establish themselves there. These endo- 

 phytic Nostoc-colonies are constant features 

 in all species of Anthocerotales. 



FIG. 181. A, Lejeunia sp., show- 



a West Indian Lejeunia, the 

 lower leaf-lobes, x, modified into 

 water sacs (X 75). 



Reproduction 



The reproductive organs are formed 

 together upon the dorsal surface of the 

 thallus much as in Riccia, but they differ 

 in certain respects from those of the true 

 Hepaticse, and suggest rather those of the 

 lower Pteridophytes. 



Antheridium. The antheridium (Fig. 

 184) is always formed endogenously. A 

 superficial cell divides by a transverse wall 

 into an outer and an inner cell, of which the 



ing the ventral leaves, or amphi- i atter develops into the antheridium or may 

 gastria, am (X about <H>). B, diyide further? so M to produce a group of 



antheridia lying within a closed cavity. The 

 mature antheridium is an oval or globular 

 body borne upon a stalk, which in some 

 species of Dendroceros becomes very long. The wall of the antheridium is com- 

 posed of a single layer of cells, each containing a chromatophore, which often 

 assumes a red or yellow color at maturity. 



Archegonium. The archegonium mother-cell does not project above the 

 surface of the thallus, and it remains very inconspicuous, the outer neck-cells 

 not being clearly distinguishable from the adjacent thallus-cells, and the egg- 

 cell being some distance below the level of the thallus, as is the case in the 

 Ferns. 



The Sporophyte 



The sporophyte in the Anthocerotales differs very much from 

 that of the Hepaticse. The archesporium, or sporogenous tissue, is 

 reduced to a single primary layer of cells, which later divides into 

 two, or in Notothylas into four. 



The first divisions in the embryo (Fig. 185) result in several tiers of cells, 

 which become next divided by periclinal walls into a central part, the "Endo- 

 thecium," and an outer portion, the " Amphithecium." The endothecium takes 

 no part in spore-formation, but persists as a central strand of tissue, the colu- 



