FUNCTION.] ORGANS FOR SECRETION". 307 



purpose. They have been examined by M. Trinchinetti, who 

 describes them to be small bodies, sometimes conical, some- 

 times globular, either naked or hairy, and sometimes defended 

 by a spine. He names them periphylls because they chiefly 

 occur near the periphery, or circumference of a leaf. They 

 vary, however, greatly in appearance, as has been shown in 

 the first volume when speaking of glands. One of the most 

 common forms is that which occurs among the phyllodineous 

 Acacias. Unger states that in Acacia longifolia, at the base 

 of the lamina or of the phyllode, and on its upper edge, " a 

 small impression is remarked in the form of a point, which is 

 the orifice of the excretory canal of a cavity existing in the 

 substance of the organ. This cavity is not hollowed in the 

 ordinary parenchym, but is surrounded entirely by peculiar 

 cells with small and thin walls, the whole constituting a sort 

 of glandular apparatus, shaped like a kidney-bean, bulky, and 

 almost as large as a third of the phyllode. It is surrounded 

 by several vascular bundles, and has direct relations with 

 four of them. The cells which form the gland contain no 

 solid matter ; but those which surround this apparatus contain 

 granules of starch, which become more numerous and larger 

 in proportion to their distance. The liquid which fills them is 

 turbid, which shows its state of concentration. On examining 

 it with the aid of some re-agents, Unger found that it contains, 

 besides sugar, a second substance, which is gum or vegetable 

 mucilage. From this and other observations M. Unger infers 

 that the nectariferous glands of leaves exhibit in their essential 

 structure a great analogy with one another and that the 

 production of sugar is effected in all in the same manner. 



In many plants, however, the secretions are effected with- 

 out the assistance of any apparent glandular apparatus. 

 According to Morren the fat or fixed oils are merely formed 

 in cells, while the volatile oils are secreted in glands formed 

 for the express purpose. This is, however, denied by Link, 

 who asserts that in general volatile oil is deposited in the com- 

 mon cells of the plant, where it appears more or less plainly 

 in the form of small oily drops among the sap, or even in large 

 masses. This is almost always the case in the petals, and 

 it is very rare that the oil is secreted in internal glands. 



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