ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
367 
Although occupying the position of leaf-structures, they are of purely 
epidermal origin, and consist entirely of parenchymatous cells without 
any vascular elements. These organs present therefore a further 
illustration of transitional structures intermediate between pliyllomes 
and trichomes. They also occur on the bud-scales, and are apparently 
in all cases functionless. 
Pearl-glands. — According to Prof. O. Penzig,* these structures vary 
in their morphological value in different instances. In the Piperacese 
and Begoniaceae they are trichomic, in the Ampelideas they are emer- 
gences. Their structure in the case of the grape-vine is described in 
detail. The epiderm of the gland is usually furnished with a stomate. 
The cells contain drops of oil and small granules of starch and pro- 
teinaceous substances. They appear to furnish food for Acari. 
Dr. A. Nestler f describes the structure of the remarkable spherical 
glands which, under certain conditions, produce a pearl-like appearance 
on all the aerial organs of Artanthe cor difolia. They are simply pro- 
tuberances from special epidermal cells. Within them were found 
protoplasmic threads and a fatty oil. 
Achenial Hairs of Compositse.f — Miss M. A. Nichols has examined 
the structure of the hairs on the achene of a large number of American 
Composite. She finds two types of hair, which do not closely corre- 
spond to the established lines of group division, viz. : — (1) a simple 
pointed hair having apparently no median line or division-wall ; (2) a 
compound or double hair, branching so as to form a double-pointed 
apex. 
Hairs of Tilia argentea.§— Herr von Widenmann points out a 
remarkable connection between the hairy covering of the leaves of the 
silver lime and the production of fruit. The purpose of this covering 
seems to be the protection of the leaves in their pendent position, which 
is necessary in order to allow a sufficient access of air and light to the 
flowers to permit of the development of the fruit. 
Classification of Tubers. || — M. B, Clos proposes a classification of 
tubers into four classes, viz. : — (1) Germination-tubers (present in the 
earliest stage of the plant) ; (2) Gemmation tubers (formed at a later 
period) ; (3) Pseudorhizal tubers (formed on adventitious roots) ; 
(4) Tubers of the ascending axis. The first two classes are again 
divided into a number of sub-classes. A list is also given of the species 
of Leguminosse on which the root-tubers have been observed. 
j3. Physiology. 
Cl) Reproduction and Embryology. 
Embryo-sac of Acer rubrum.^T — Mr. D. M. Mottier has followed out 
the development of the embryo-sac in this tree, and finds that it presents 
* Atti Congr. Bot. Internaz. Genova, 1892 (1893) pp. 237-45 (1 pi.). See Bot. 
Centralbl., lvii. (1894) p. 76. 
t Oesterr. Bot. Zeitschr., xliii. (1893) pp. 333-5, 386-90 (1 pi.). 
t Bot. Gazette, xviii. (1893) pp. 378-82 (1 pi.). 
§ J. Heft. Yer. Yaterl. Naturk. Wiirttemberg, xlix. (1893) 6 pp. and 1 pi. See 
Bot. Centralbl., lvii. (1894) p. 141. 
|| Mem. Acad. Sci. Toulouse, v. (1893) pp. 381-405. 
^ Bot. Gazette, xviii. (1893) pp. 375-7 (1 pi.). 
