ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
703 
reserve-substances have a similar distribution, and there appears to bo 
an intimate relationship between the two classes of substances. They 
have, however, an entirely independent origin ; in fruits, leaves, stems, 
&c., the fatty oils are not accompanied by albuminoids. The former are 
produced within the green protoplasm. The disappearance of the 
reserve oily substances is not the work of any special diastase (saponase). 
In the seeds of grasses, on the other hand, which may be regarded as 
oily seeds with an external reserve of starch, the starchy substances are 
assimilated by a diastase (amylase) elaborated in a special epiderm. 
The essential oils of plants were studied in a great number of 
species belonging to many natural orders. In the flower, they are 
usually found localized in the epidermal cells of the upper or under 
surface of the petals or sepals ; in the leaf, in the epidermal cells of the 
upper surface; in the stem and fruit, in the epiderm. They appear 
always to originate in the chlorophyllaceous protoplasm, passing through 
the intermediate stage of tannoid substances. In its decomposition the 
chlorophyll gives rise also to other substances, such as tannins, latex, 
pigments, &c. Hence white petals, in which the transformation into 
essential oils has been the most complete, are often the most strongly 
scented ; while brown and orange petals, in which pigments have been 
produced in large quantities, are more frequently scentless. 
Localization of Alkaloids.* — M. G. Chautriau distinguishes five 
types in the mode of distribution of alkaloids in plants, viz. : — (1) In a 
layer of cells lying between the endosperm and the true testa (Atropa 
Belladonna , Batura Stramonium , Hyoscyamus niger) ; (2) in two layers 
(especially in the outer one) between the endosperm and the pericarp ; 
also, to a smaller extent, in the epiderm and in the cells which accom- 
pany the vascular bundles (Gonium maculatum) ; (3) in the endosperm, 
especially in its peripheral cells ( Aconitum Napellus, Delphinium Staphi- 
sagria ) ; (4) in all the cells of the endosperm, and to a smaller extent 
in those of the embryo ( Strychnos Nux-vomica) ; (5) apparently in the 
cotyledons and plumule (Lupinus albus). 
The alkaloids take no active part in germination, but are formed in 
the seedling from decomposition of the albuminoids. 
In Papaver somniferum the amount of alkaloids decreases as the seeds 
ripen, and this is accompanied by an elimination of nitrogen. As in 
the other plants examined, they are not used by the plants as nutritive 
substances ; their main function is protection against animals. 
Formation and Function of Tannins.f — Herr G. Mielke disputes 
the statement that tannic acids are ever produced out of albuminoids. 
The previous stages of their formation are phenols, phenol-alcohols, 
aldehydes; these occur, in chemical combination with sugar, as gluco- 
sides, and play an important part in vegetable economy, since they are 
the indispensable materials for the production of lignifying substances. 
True tannins are stored up only in small quantities in vegetable tissues ; 
they can take part in metastasis only when they revert to their previous 
stages by absorption of water. Resins and essential oils are probably the 
final results of the metamorphosis of tannins. 
* Bull. Soc. Beige Micr., xviii. (1894) pp. 33-54. 
t Progr. d. Realsch. v. d. Holstenthore in Hamburg, 1893, 38 pp. See Bot. Cen- 
tralbl., lix. (1894) p. 280. 
