530 L1FE-I1I8T0KIES 



cylinder which consists of cells elongated in the direction of the 

 axis and with pointed ends which interlock. Such a tissue is termed 

 prosenchynia ' in contrast with pareuchyina 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 J 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 aerated. Whereas in the sporophj^te 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 the two classes liverworts (Hepaticae) 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 algffi more or less like Coleochaete, 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 Anthoccros type which solves the problem of uj)- 

 lifting its spores in the simplest way. Various more or less com- 



^ Pros-en 'chy-ma< Gr. pros, before; en, in; cheo, pour. 



^ Par-en'chy-ma < CJr. para, beside. A term applied by the earlier 

 anatomists to the main tissue of sueh organs as the lungs which they 

 supposed was formed of material poured in beside tlie vessels and nerves 

 that had been " poured in " before. 



' Ep-i-dcr'mis < Gr. epi, upon, t. e., outer; derma, skin. 



* Cor'tex < L. cortex, rind or bark. 



^Sto'ma< Gr. .s7o/««, a mouth. 



