296 



BOTANY 



TAUT I 



The i-upture of ripe seed-vessels, as well as their dehiscence by the opening of 

 special apertures {Papaver, Lychnis, Antirrhinum, etc.) is a consequence of the 

 imequal contraction of the cell-walls due to desiccation. At the same time, by 

 the sudden relaxation of the tension, the seeds are often shot out to a great distance 

 (Tricoccae, Geranium, etc.). In certain fruits not only curvatures but torsions are 

 produced as the result of changes in the amount of water they contain, e.g. Erodium 

 (jriiinum (Fig. 224), Stipa picnnata, Avena stcrilis ; by means of these, in conjunc- 

 tion with their stiff barb-like hairs, the seeds bury themselves in the earth. 



The opening or closing of the moss sporo- 

 gonium is, in like manner, due to the hygro- 

 scopic movements of the teeth of the peri- 

 stome surrounding the mouth of the capsule. 

 In the ease of the Equisetaceae the outer 

 walls of the spores themselves take the form 

 of four arms, which, like elaters, are capable 

 of active movements ; by means of these 

 numbers of spores become massed together 



A 



Fig. 224. — Partial fruit of Erodium gruinum. 

 A, in the dry condition, coiled ; B, moist 

 and elongated. 



Fig. 225. — Diagram of a cohesion curvature. 1. Cells 

 in original position. 2. After partial evaporation 

 of the water lilling them (w) ; the upper eell-wall 

 (()) is curved in, while the lower (u) retains its 

 original length. 



before germinating, and the isolation of the dioecious prothallia prevented (Fig. 

 408 E). 



Similar movements of no use are also met with, thus dead branches of Conifers 

 exhibit the most beautiful hygroscopic movements. 



In order to call forth imbibition movements the actual presence of liquid water 

 is not necessary, for the cell-walls have the power of al)sorbing moisture from the 

 air. They are hygroscopic, and are used to estimate the humidity of the air in 

 hygrometers and weather-glasses. 



Steinbrinck and Kamerling have distinguished the mechanisms 

 which depend on the cohesive power of water from those depending 



