ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 77 



Secondary Thickening in the Aerial Roots of Ivy.* — Prof. R. J. 

 Harvey Gibson notes a singular change which has taken place in the 

 aerial roots of a plant of ivy. The number of protoxyiems is greatly 

 increased ; the pericycle is much thicker ; the endoderm is well marked, 

 and is followed by a thick cortex. As the root becomes older, two 

 cambiums make their appearance in a manner quite similar to that seen 

 in a normal underground dicotyledonous rout. 



Histological Changes produced by Phytoptus.t — From an exami- 

 nation of the twigs of the pear infested by galls produced by Phytoptus 

 pyri, M. M. Molliard draws the conclusion that the chemical irritation 

 resulting from the action of parasites, such as the Pliytoptidaa, deter- 

 mines the formation of a new tissue which is differentiated at the expense 

 of cells of any kind, whatever may be their future development under 

 ordinary conditions ; this new tissue being destined for the nourishment 

 of the parasite. In the case under discussion this new tissue consists 

 of a number of layers, which may amount to as many as fifteen, of homo- 

 geneous cells immediately beneath the bark. The phelloderui consists 

 of several layers of cells either entirely destitute of starch, or containing 

 only very small grains. 



Raphid-Cells.| — Herr F. G. Kohl has investigated the structure and 

 •development of raphid-cells. chiefly in Hyacinthus and in the Orchideae. 

 The bundle of raphids is enveloped in a protoplasm-sac, not only when 

 young, but for a considerable time. This sac is usually suspended by 

 two strings of protoplasm lying in the direction of the axis of the bundles, 

 and it is connected ulso witn the parietal protoplasm by fine protoplasmic 

 filaments. The nucleus of the raphid-cells is usually parietal. The 

 separate crystals are for a long period enveloped in sheaths of cytoplasm, 

 which display the same staining and micro-chemical reactions as the 

 parietal protoplasm and that of the strings. The mucilage of the 

 raphid-cells always fills up the vacuoles, and is permeated by strings 

 of protoplasm. B >th the parietal protoplasm of the raphid-cells of the 

 tubers of Orchis and the protoplasm of the central sac have a reticulate 

 structure on the inner or outer side. The mucilage of these cells is 

 chiefly formed out of starch ; but in the mature cells there are usually 

 only traces of normal starch. 



Oil-Cells and Oil. § — Herr R. Biermann gives an account of the 

 structure and development of oil-cells and the formation in them of 

 oil, in Cinnamomum Cassia, Laurus rubilis, Myristica fragrans, and other 

 plants. In their early stages there is no difference in the mode of 

 formation of oil-cells and of mucilage-cells ; the first stage in both is 

 the formation of mucilage-membranes. The resiuogenous layer re- 

 sembles protoplasm in being stained yellow or brown by iodine, but 

 differs from it in its capacity of taking up certain anilin pigments, 

 •especially methyl-green, and not giving them up again to solvents. 



• Prcc. and Trans. Liverpool Biol. Soc, xiii. (1899) pp. 185-7 (1 pi.), 

 t Cumptcs Rendus, exxix (1S99) pp. 841-4. 

 t Bot. Centralbl., lxxix. (1899) pp. 273-S2 (1 pi. and 6 figs.). 

 § Arch. d. Pharmacie, cexxxvi. pp. 74-80. See Beih. z. Bot. CLutralbl., ix. 

 (1899) p. 15. 



