No. II.] THE BRYOPHYTES OF CONNECTICUT. 21 



this fact is sometimes difficult to demonstrate. They are desti- 

 tute of midribs, but show a remarkable differentiation into two 

 kinds of cells : — green cells, which remain alive for a long 

 time ; and colorless cells, which soon lose their living contents 

 and become empty. In the leaves of the spreading branches 

 the green cells are united in such a way that they form a 

 loose network, each mesh of which is filled with a single 

 large colorless cell. The latter is characterized by a thin wall, 

 usually with band-like thickenings on the inside which keep 

 it from collapsing, and by holes or pores which place its 

 cavity in direct communication with the outside. The stems 

 and branches are usually covered over on the outside by a 

 cortex composed of similar colorless cells ; within this is a 

 distinct zone of sclerenchyma enclosing a central pith. The 

 tufted habit of the peat mosses, their upright stems covered 

 with pendent branches, and their porous hyaline cells, account 

 for the ease with which they suck up and retain water. The 

 process is largely due to capillarity. 



The archegonia are borne at the tips of branches, and 

 limit their growth just as in the Jungermanniacese. The 

 sporophyte consists of a spherical capsule and a broad foot 

 with a deep constriction between them. No true stalk is 

 developed. The calyptra persists until the spores are mature, 

 and is then irregularly ruptured by the dehiscence of the 

 capsule. The latter while still immature contains a large 

 columella in the form of a hemisphere. This is covered over 

 at the apex by the small spore cavity in much the same way 

 as in the Anthocerotales, but the cavity contains spores only. 

 The wall of the capsule is several cells thick, the outer layer 

 forming a distinct epidermis. Some of the inner cells contain 

 chloroplasts, but there are no intercellular spaces among them, 

 and the epidermis develops no effective stomata, so that the 

 wall can hardly serve as a very useful photosynthetic tissue. 

 When the spores are mature, the upper part of the archegonial 

 branch elongates rapidly, thus simulating a stalk, and the 

 capsule opens by means of a circular split in the wall, which 

 cuts off a cap-like lid. As the drying of the capsule proceeds, 

 the pressure in the interior increases, until a sudden liberation 

 takes place which shoots out the spores together with the 



