604 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Mai-cliantiaceffi, Gyathodiim has globular cells on the upper surface, 

 which allow of a concentration of light on the chlorophyll-grains lying 

 below. This causes also a partial "reflection of light, and thus, like 

 Schistostega, it glows with an emerald-green light. In Jungermanniacete 

 the plants react to a weak illumination by enlargement of the leaf- 

 surface, convexity of the cells, and hehotropic curvature. Adapta- 

 tions to protection from light are much more frequent, and have been 

 indicated as xerophytic adaptations, which are also to be found. 

 Absorption of red and yellow light- rays takes place in red-brown, 

 violet, and sometimes almost black liverworts, in which the coloration 

 is limited to the cell-wall (regarded by Stahl as an arrangement for 

 storing up warmth). Marchantiaceffi of the Mediterranean region, 

 which have violet scales on the lower surface of the thallus (Tarffionia, 

 Grimddia dichotoma), protect themselves from superfluous light by 

 an incurving of the thallus. A yellowish colouring of the walls of the 

 epidermis cells should hinder the passing of blue and violet rays. 

 Reflection of the light by dead, air-conducting cells, which give the 

 plant a silver-grey appearance, occurs in many liverworts of the high 

 mountains, as, for instance, Gymnotrichium, Anthelia, and others. In 

 these the upper free-standing portion of the imbricating leaves is 

 dead. A glittering wax-like surface occurs in species of Flagiochasma 

 and Marchantia. In species of Riccia a cell void of chlorophyll is found 

 at the apex of each of those columns in which the assimilation-cells are 

 arranged. In R. melitmsis there are as many as four to five. The re- 

 flection of the light-rays, entering by this means, causes the surface of 

 the thallus to appear whitish-green. The formation of cilia and 

 bristles serves also to diminish the light. An interesting analogy is 

 seen between the fenestrate leaves of 3Iesembnjanthemum and the 

 fenestrate thallus of Ricciacese, in which the above-mentioned epidermis 

 cells, devoid of chlorophyll, are more or less closely adpressed, while the 

 columns of chlorophyll cells have wide intercellular spaces. Light can- 

 not easily penetrate through the openings between the epidermis cells. 

 In Riccia Sommieri the light- and air-channels are still further limited 

 by a layer of cells with thickened walls below the epidermis. Exor- 

 tnotheca Welwitschu from Algiers shows the most interesting structure. 

 The basal tissue, filled with oil as reserve material, is entirely buried m 

 the ground. Then comes the lower assimilative tissue, and, upon that, 

 high air-chambers which are surrounded by cells with pale yellowish 

 wails and clear contents and stomata above, which act also as windows 

 for light. The hght can also reach the assimilative tissue reflected, 

 filtrated, and broken. The principal function of these air-chambers, 

 apart from transpiration, would seem to be to. give protection from 

 intensive light. 



Duration of Sporogonial Development in Mosses."— W. Krieger 

 publishes the results of his investigations on the time of development 

 of sporogonia in :— 1. The same moss, in a similar habitat, in one year. 

 2. The same moss, in a similar habitat, in the course of several years. 



* Inaug. Dissert. Univ. Miinster (Dresden, 1915) pp. 1-51. See also Bot. 

 Centralbl., cxxxiv. (1917) pp. 55-6. 



