530 - LIFE-HISTORIES 
cylinder which consists of cells elongated in the direction of the 
axis and with pointed ends which interlock. Such a tissue is termed 
prosenchyma } in contrast with parenchyma 2 which is composed of 
cells not much elongated, and without pointed ends, as is the case 
with nearly all the tissues we have so far studied. At the surface 
of the sporophyte is a protective layer of cells, distinguished as the 
epidermis; 3 the looser, mostly green tissue which lies between the 
epidermis and the central cylinder being termed the cortex.4 In the 
epidermis near the base of the capsule occur peculiar openings called 
stomata * communicating with the internal air-spaces of the cortex. 
Each opening is guarded by two special cells which might be likened 
to lips. It is by means of these breathing pores that the interior 
tissues are aérated. Whereas in the sporophyte of Sphagnum we 
have a very simple sporangium from which there is differentiated 
a small foot and the merest hint of a short connecting stem; in Fu- 
naria we find a long slender stalk, homologous with the foot, bearing 
a capsule made up of the sporangium partly inclosed by an urn-like 
mass of tissue which we may call the shoot. Funaria represents 
about as high development of the sporophyte as moss plants have 
ever attained. 
191. The bryophyte division, mossworts (Bryophyta) 
comprises only tthe two classes liverworts (Hepatice) and 
true mosses (Musci) which in general are often called moss- 
worts. 
Mossworts show us possibly how green earth-plants first stood 
upright. The occasion for their vertical development may have 
arisen when certain flat alge more or less like Coleochete, became 
stranded and had to form spore-cases as best they could before the 
mud completely dried. If some of them were able to make a small 
globular capsule this might be fed entirely by the thallus, but being 
immersed within it could not ordinarily scatter the spores very far. 
Their descendants perhaps give us Riccia. Others we may suppose, 
hit upon the plan of elongating the capsule upward, giving it some 
chlorophyll to utilize the sunshine, and thus enable it to make more 
spores and scatter them farther—all with much less dependence 
upon the slender resources of the little nurse. The result would be a 
liverwort of the Anthoceros type which solves the problem of up- 
lifting its spores in the simplest way. Various more or less com- 
1 Pros-en’chy-ma< Gr. pros, before; en, in; cheo, pour. 
2 Par-en’chy-ma < Gr. para, beside. A term applied by the earlier 
anatomists to the main tissue of. such organs as the lungs which they 
supposed was formed of material poured in beside the vessels and nerves 
that had been “ poured in ”’ before. 
8 Ep-i-der’mis < Gr. epi, upon, 7. e., outer; derma, skin. 
4 Cor’tex < L. cortex, rind or bark. 
5 Sto’ma< Gr. stoma, a mouth. 
