. An introduction to vegetable physiology. Plant physiology. 112 VEGETABLE PHYSIOLOGY made to emerge from its cut surface in a continuous stream by reducing the pressure above the water by means of an air-pump. The facility of the interchanges will largely depend upon the number, size, and position of these orifices. A lenticel will allow more gas to pass between its loosely arranged cells than will a stoma, but their relative numbers make the stomata much more important than the lenticels. In most cases there is a free passage through the stomatal pore, but in others considerable difficulty i
. An introduction to vegetable physiology. Plant physiology. 112 VEGETABLE PHYSIOLOGY made to emerge from its cut surface in a continuous stream by reducing the pressure above the water by means of an air-pump. The facility of the interchanges will largely depend upon the number, size, and position of these orifices. A lenticel will allow more gas to pass between its loosely arranged cells than will a stoma, but their relative numbers make the stomata much more important than the lenticels. In most cases there is a free passage through the stomatal pore, but in others considerable difficulty is afforded by the aperture being sunk in the epidermis or situated in a. Fig. 81.—Transvekse Section of Eolled Leaf of Heath. depression of the leaf. In the rolled leaves of heaths and certain grasses this difficulty is frequently partially com- pensated by the lacunar character of the parenchyma which is in the immediate neighbourhood of the stomata (fig. 81). It must be noted in this connection that the stomata and the lenticels are passive with regard to the process of aeration, and do not exert an active influence upon it. The variations in the width of the stomatal apertures which are of so much importance in the regulation of transpiration must be regarded as bearing upon that function alone, being caused by fluctuations in the amount. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Green, J. Reynolds (Joseph Reynolds), 1848-1914. Philadelphia, P. Blakiston
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