BRYOPHYTA. 



95 



looks something like a flower. (This is still more evident in 

 some other mosses. See Figure 65, E, F.) 



The leaves when magnified are 

 seen to be composed of a single layer 

 of cells, except the midrib, which is 

 made up of several thicknesses of 

 elongated cells. Where the leaf is 

 one cell thick, the cells are oblong in 

 form, becoming narrower as they ap- 

 proach the midrib and the margin. 

 They contain numerous chloroplasts 

 imbedded in the layer of protoplasm 

 that lines the wall. The nucleus (Fig. 

 63, (7, ri) may usually be seen with- 

 out difficulty, especially if the leaf 

 is treated with iodine. This plant is 

 one of the best for studying the di- 

 vision of the chloroplasts, which may 

 usually be found in all stages of divis- 

 ion (Fig. 63, D). In the chloroplasts, 

 especially if the plant has been ex- 

 posed to light for several hours, will 

 be found numerous small granules, 



that assume a bluish tint on the application of iodine, showing them 

 to be starch grains. If the plant is kept in the dark for a day or two, 

 these will be absent, having been used up ; 

 but if exposed to the light again, new 

 ones will be formed, showing that they 

 are formed only under the action of light. 



Starch is composed of carbon, hydro- 

 gen, and oxygen, and so far as is known 

 is only produced by chlorophyll-bearing 

 cells, under the influence of light. The 

 carbon used in the manufacture of starch 

 is taken from the atmosphere in the form 

 of carbonic acid, so that green plants serve 

 to purify the atmosphere by the removal 

 of this substance, which is deleterious to 

 animal life, while at the same time the 

 carbon, an essential part of all living 



FIG. 59. Longitudinal section 

 through the summit of a small 

 male plant of Funaria. a, a', 

 antheridia. p, paraphysis. L, sec- 

 tion of a leaf, x 150. 



FIG. 60. A, S, young anthe- 

 ridia of Funaria, optical 

 section, x 150. C, two sperm 

 cells of Atrichum. D, sper- 

 matozoids of Sphagnum. 

 x600. 



