ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
499 
The author concludes that the presence and the distribution of 
crystals of calcium oxalate are not connected with physiological pro- 
cesses in the plant, but rather with its genetic relationships. 
Silica in Plants.* — MM. Berthelot and G. Andre have instituted a 
series of experiments for the purpose of determining the proportion 
of silica, and the mode in which it occurs, in different stages of de- 
velopment in plants. The observations were made on wheat, the grains 
of which contain scarcely a trace of silica. The grains were sown on 
April 15. On April 30 the greater part of the silica contained in 
the stem was in the insoluble state, and must therefore have under- 
gone a transformation after its absorption. On June 12, on the other 
hand, the chief part of the silica was soluble in alkalies. On June 30 
at the commencement of blossoming the proportion of silica present 
was largest in the leaves, smallest in the inflorescence ; the former 
was chiefly in the insoluble, the latter in the soluble condition. On 
July 23 the results were nearly the same. An examination of dried 
plants on August 18 showed that the amount of silica had increased 
considerably in the stem and leaves, but only slightly in the ear. 
(3) Structure of Tissues. 
Formation of Annual Rings.f — Prof. R. Hartig replies to some of 
Jost’s criticisms on his explanation of the increase in thickness and 
formation of annual rings in dicotyledonous trees, and adduces further 
arguments in its support. He maintains that the number, size, and 
distribution of the vessels in the annual ring are in direct dependence 
on the area of the transpiring leaf surface, and on the amount of 
nutrient cambium formed. This applies to the formation of all the 
conducting elements in the interior of the plant, — vessels, tracheids, &c. 
Bicollateral Bundles of Cruciferse.f — Prof. A. Borzi has investi- 
gated the development and structure of the anomalous bicollateral vas- 
cular bundles in the stem and root of Cruciferse with woody stems 
( Brassica fruticulosa and Erucastrum virgatum). The bundle contains 
an internal portion of a phloem-character, and is therefore bicollateral 
in the true sense of the term. The internal xylem usually originates 
from the primitive meristem ; but the cambium may form new phloem- 
elements in centrifugal succession, which increase the size of the 
original bundle. The cambium retains the power of generating centri- 
fugally new layers of secondary phloem, in the form either of con- 
tinuous or of more or less interrupted zones concentric with the axis. 
These layers remain attached to the secondary xylem and inclosed within 
it. In B. fruticulosa some of the bundles are deficient in the internal 
phloem, and the primary xylem is reduced to a small number of woody 
fibres, spiral vessels being entirely wanting. The root (in B. fruticulosa) 
exhibits a similar structure ; the vascular bundles have bands of internal 
phloem due to the original activity of the cambium, which gives birth 
later to layers of secondary phloem, forming zones within the xylem. 
* Comptes Rendus, cxiv. (1892) pp. 257-63. 
t Bot. Ztg., 1. (1892) pp. 176-80, 193-6. Of. this Journal, 1891, p. 761. 
X Malpighia, v. (1892) pp. 316-31 (2 pis.); and Bull, Soc. Bot. Ital., i. (1892) 
p. 60. 
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