. Carnegie Institution of Washington publication. IO THE PHYSIOLOGY OF STOMATA. extent of opening to the same scale. Roughly speaking, the transverse form may be described as elliptical, but this is departed from in the acute apices and flattened sides, the departure being greatest in regard to the apices in the smaller openings and in the sides in the larger. The plastids of the guard-cells are numerous and very faintly green. The size of the plastid varies with the amount of contained starch, and this doubtless modifies the optical effect of the chlorophyll upon the eye. Even when the amount
. Carnegie Institution of Washington publication. IO THE PHYSIOLOGY OF STOMATA. extent of opening to the same scale. Roughly speaking, the transverse form may be described as elliptical, but this is departed from in the acute apices and flattened sides, the departure being greatest in regard to the apices in the smaller openings and in the sides in the larger. The plastids of the guard-cells are numerous and very faintly green. The size of the plastid varies with the amount of contained starch, and this doubtless modifies the optical effect of the chlorophyll upon the eye. Even when the amount of starch is low the amount of green color is very small, so that the plastids appear almost colorless. The contrast between the chlorenchyma plastids and those of the guard-cells is in this regard very striking, as also is the difference in the origin and development of the starch granules. In the chlorenchyma plastids the starch appears as small lenticular bodies, two to three or four in number, but never large enough to modify the form of the plastids in which they occur. In the guard-cell, however, the starch granules are spherical, except for the contigu- ous flattened facets caused by mutual contact. They are, moreover, so large that the plastids, when fully loaded with starch, appear as a compound starch grain, such as occurs in certain cereals, while the matricial substance can scarcely be detected. The application of Molisch's (1896) potash test shows a pronounced reac- tion, but while the plastids of the chlorenchyma retain their individu- —Transverse sections of stomata of. Fouquie- &-^ f^OSe of the gUard-Cells do not. ria splendens. Two stomata, one closed and , ... r , the other open, drawn to the same scale. The ThlS may be due to the Swelling Ot the black square represents 40 micra on each side. s^-arcJj and Consequent disorganization of the plastids, which, being crowded together in this condition, would pro- duce a general coloring effect rather th
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