650 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Mineral Food-ingredients of Plants. * * * § — Herr O. Loew discusses 
several questions in connection with the supply of mineral food-sub- 
stances to plants. Magnesium salts by themselves are poisonous to the 
plant, and can contribute to its nutrition only in the presence of calcium 
salts. Calcium, on the other hand, is essential to all the higher plants 
(not to Fungi), and exercises no injurious influence ; but the presence 
of magnesium also is essential. 
Calcium Oxalate in the Leaves of Conifers.f — Prof. K. Wilhelm 
finds crystalline calcium oxalate abundantly in the walls of the paren- 
chymatous cells of the leaf in many Abietineae, but not in Larix. The 
crystals were found also in the cell-cavity. In the cuticle of the upper 
surface of the leaf of Pinus montana he observed peculiar granular 
doubly refractive bodies, soluble in chloroform, as well as spherites in 
some of the epidermal cells. 
(3) Structure of Tissues. 
Assimilating Tissue. J — In the opinion of Sig. L. Montemartini, the 
palisade-parenchyme is not the specific assimilating tissue of plants, not 
being adapted for any great activity in the chloroplasts which it contains. 
Observations, chiefly on Opuntia , lead him to the conclusion that, under 
similar conditions, the chloroplasts are more active in a spongy than in 
a palisade parenchyme, the access of carbon dioxide being more difficult 
in the latter. 
Phloem-islands in the Xylem of Stryehnos.§ — M. L. Sauvan has 
investigated the origin of these structures in both the stem and root of 
StrycJmos nux-vomica , and finds the phenomena to be the same in both 
cases. As to their mode of origin, he supports the conclusions of 
Herail, Scott, and Brebner,|| rather than those of Perrot.^l The inclu- 
sion of phloem-islands in the xylem is the result of an irregular function 
on the part of the generating layer, which ceases to produce xylem, and 
then of the formation of a complementary cambium. This complemen- 
tary cambium frequently arises in the midst of the phloem-tissue, and 
produces a layer which gives birth to both phloem and xylem. The 
continuity of this layer with the normal cambium is only apparent. 
The medullary rays are continued, not only across the phloem-island, 
but also across the new cambium zone, and are then lost in the phloem- 
tissue. The complementary cambium appears to be formed by septa- 
tion of the cells of the secondary phloem-parenchyme. 
Vittae of the TJmbelliferae.** — M. C. van Wisselingh has studied the 
nature of the cell-wall, and the mode of formation of the secretion, in 
the vittas of a large number of Umbelliferas, and his conclusions differ 
* Bot. Centralbl., Ixiii. (1895) pp. 161-70. Cf. this Journal, ante, p. 545. 
t SB. Vers. Deutsch. Naturf. u. Aerzte, 1894. See Bot. Centralbl., lx. (1894) 
p. 198. 
X Atti 1st. Bot. R. Univ. Pavia, iv., 40 pp. and 1 pi. See Bot. Contralbl., Ixiii .. 
(1895) p. 74. 
§ Journ. de Bot. (Morot), ix. (1895) pp. 266-73 (7 figs.). 
|| Cf. this Journal, 1886, p. 1010; 1890, p. 199. 
i Cf. this Journal, ante, p. 445. 
** Arch. Neerl. Sci. Ex. et Nat., xxix. (1895) pp. 199-232 (2 pis.). 
