ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
361 
ptyalin, diastase, and emtilsin wero also used. The points they directed 
their attention to were : — the effect of temperature ; the action of sunlight, 
of gases, and of various chemicals ; the effect of filtration and dialysis ; 
the mutual action of ferments ; their fate within the organism ; and lastly, 
their supposed poisonous properties. Contrary to the opinion of all pre- 
ceding writers, the authors state that the enzymes are not poisonous, 
even when 2 grm. are injected daily for a week, and they state that the 
poisonous effect attributed to enzymes must have been due to the presence 
of microbes. 
Localization of the Active Principles of the Cucurbitacese.* * * § — 
M. L. Braemer finds the bryonin of Bryonia dioica, the colocynthin of 
Citrullus Colocynthis, and the elaterin of Ecbalium Elaterium , located in 
special elements which have the form of tubes arranged in straight or 
curved rows, and situated chiefly in the periphery of the liber, the peri- 
cycle, and the cortical and fundamental parenchyme. They differ alto- 
gether from normal sieve-tubes, and more nearly resemble laticiferous 
tubes of the septated type. 
Localization of Nicotine in the Tobacco-plant.f — Dr. G. B. De Toni 
has investigated the occurrence of nicotine in Nicotiana Tabacum and 
other species of the genus. The alkaloid does not occur in the seeds 
nor in the very young plant. In the root of the mature plant it is found 
in the cortical tissue. In the aerial organs — branches, leaf-stalk, lamina, 
calyx, corolla — it is chiefly localized in the epiderm, and especially in 
the basal cells of the hairs. It was not found in the mesophyll or 
assimilating tissue of the leaf. The author does not regard nicotine as 
having any defensive function ; it appears to be an excretory product, 
the result of a process of deoxidation. The various micro-chemical 
reactions are given. 
Fatigue-substances.J — By the name “fatigue-substances” (Ermud- 
ungsstoffe) Herr F. Beinitzer proposes to designate those bodies which 
are thrown off from the plant, and which act in a restraining or poisonous 
manner on its own life. With the Schizomycetes and Saccharomycetes 
these substances often entirely prevent the further growth of the 
organism from which they are thrown off. But in the higher plants they 
are generally found in special receptacles separated from the living tissue 
by impermeable walls. Here they may serve a secondary and useful 
purpose in the life of the plant, by shielding it from the attacks of 
enemies which would otherwise destroy it. 
(33 Structure of Tissues. 
Perimedullary Zone.§ — As the perimedullary |] zone of the stem M. L. 
Flot defines the peripheral region of that portion of the inner tissue 
which is bounded outwardly by the protoxylem. When the vascular 
bundles are not united by a continuous cambium ring, this zone is 
visible only on the inside of the bundle. In this case it either remains 
* Comptes Rendus, cxvii. (1893) pp. 753-4. 
f Atti R. 1st. Veneto, iv. (1893) pp. 1736-44. 
X Ber. Deutsch. Bot. Gtsell., xi. (1893) pp. 532-7. 
§ Ann. Sci. Nat. (Bot.), xviii. (1893) pp. 37-112 (4 pis.). 
|| Eedius, circummedullary. 
