Hohnesdale Natural History Club. 



nor define the nature of this adaptation, but I think it is plainly indicated 

 to us in the sensibility which some plants show to the presence of water, 

 and in the movements in them which are so readily excited by it. 

 Examples of this sensibility are seen in the spores of Equisetum, the awns of 

 Avena fatua, of Erodium moschatum, and in the pappus of compound 

 flowers. According to Mirbel and others the emission of pollen-grains from 

 the anther cells of plants is connected with and gives another illustration 

 of the operation of this special affinity of cell-membrane for water. It is 

 shown as follows : When the pollen is mature its grains become detached 

 from the anther cell, but then their great affinity for water causes them to 

 abstract it rapidly from the walls of the anther cell, which consequently 

 contracts with such force that it bursts open and expels the pollen. These 

 pollen grains so expelled give another and beautiful illustration of the same 

 law, for falling on the moist surface of the stigma they are entangled by it. 

 The grain of pollen so entangled absorbs moisture, which distends the grain 

 and leads to the protrusion of a slender membranous tube, which travels 

 down through the tissue of the stigma till it arrives at the ovule and 

 fertilises it by discharging the fovilla. "We come now to the leaves, where 

 the sap is brought into contact with the air, and being subjected to new 

 influences undergoes new changes, in all of which water plays an important 

 part. The proportion of water to other parts of the sap is regulated, special 

 arrangements for evaporation and absorption being in operation for this 

 purpose. On the one hand evaporation is controlled by a layer of cuticular 

 or epidermic cells, which is often covered by a secretion of wax. This 

 cuticle varies in thickness and character in different plants, being very 

 thick in some (as the oleander) usually growing in a hot and dry climate 

 and thinner in others growing in cool and moist places. On the other hand 

 excess of moisture is provided against by the presence of stomata, which are 

 specially designed for its escape. (I scarcely need observe that these 

 stomata are valvular openings, usually most numerous on the under side of 

 leaves, having free communications with the air-cavities of the plant.) 

 The action of these stomata has recently been shown in a very beautiful 

 manner by a writer in the Compter Rendus, by the action of a test-paper 

 prepared with perchloride of iron and chloride of palladium. This 

 paper is white when dry, but becomes black as soon as it is 

 moistened. A growing leaf placed between two folds of this paper 

 blackened it very quickly on that surface and opposite to those parts 

 at which the stomata were placed, so as plainly to prove that it was through 

 them that the moisture was exhaled. Some degree of evaporation also 

 takes place from all exposed parts of plants. Water is also absorbed by 

 leaves-fin a slight degree by the cuticular surface generally, and in a more 

 marked way by the stomata, and by the numerous hairs and asperities with 

 which they are so commonly provided.- As I have already stated in this 

 room, I believe one of the special purposes for which the hairs of plants are 

 designed is the collection of moisture from the air, in order that it may be 

 introduced into the sap ; and it is highly probable that some other epidermic 



