ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 667 



the work actually performed by the plant can be computed. The 

 resistance overcome by the transpiration current is often much higher 

 than can be measured by the suction of the transpiring shoot, and is 

 subject to extensive variations in different species and among plants of 

 the same species. Various parts of a stem differ widely in the resis- 

 tance offered, and there is consequently no ratio in the rate of trans- 

 mission of a stem under pressure and the length of stem. 



(3) Irritability. 



Conduction of Irritation in Plants.*— B. Nemec gives a resume of 

 his previous communications on this subject, and gives further evi- 

 dence of his discovery | of fibrils through which he believes that the 

 irritation is conducted, though positive evidence of this connection is 

 still wanting. As methods for observing the structure of these fibrils, 

 he recommends the following : — Fixing in picric-glacial-acetic-acid- 

 sulphuric acid, and staining by paracarmine ; also fixing in chrom- 

 acetic acid or Flemming's solution, staining by gentian-violet and 

 orange-G, and differentiating in oil of cloves. Even in living objects 

 he has detected them by slow killing in methylen-blue before the dis- 

 organisation of the fibrils. 



These fibrils have a definite sheath, and are imbedded in a special 

 protoplasmic layer. The sheath is regarded as a prolongation of the 

 parietal utricle, and readily breaks up into nucleole-like granules. 

 Transverse fibrils were found in certain cells, but not in bundles. The 

 protoplasmic strands composed of these fibrils are always in direct con- 

 nection with the nucleus, often dividing and enclosing the nucleus. 

 Nemec's observations were largely " traumatropic," i.e. were made on 

 the transmission of the irritation in wounded bulbs of the onion. 



G. Haberlandt,| while admitting the careful nature of Nemec's 

 observations, and confirming them to a certain extent, considers that 

 further evidence is required before it can be set down as established 

 that these fibrillar structures are the sole or the chief agent for the 

 transmission of irritation in plants. There are many examples of a 

 conduction of irritation through organs in which no fibrillar structure 

 has been detected : — glands on the leaf of Aldrovanda vesiculosa, tendrils 

 of Gucurbita Pepo, sensitive stamens of Opuntia vulgaris, &c. 



Phenomena of Tactic Sensitiveness.§ — W. Eothert describes in 

 great detail the results of a long series of observations on the sensitive- 

 ness of vegetable organisms to contact-irritation. Among the more 

 important are the following : — 



In addition to the examples already known — Polyphagus Euglense 

 and Gliytridium vorax — positive phototaxis (or, as the author prefers to 

 call it, prosphototaxis) was observed in another colourless micro-organism, 

 a species of Bodo. 



The term " chemo-kinetic sensitiveness," or chemohinesis, is applied 

 by the author to an arrest or an incitement to movement caused by 



* Die Eeizleitung u. d. reizleitenden Structuren b. d. Pflauzen, Jena, 1901, 

 153 pp., 3 pis., and 10 figs. See Bot. Ztg., lix. (1901) Abt. ii. p. 148; also Nature, 

 lxiv. (1901) p. 371. t Cf. this Journal, ante, p. 437. 



X Biol. Centralbl., xxi. (1901) pp. 369-79. 



§ Flora, lxxxviii. (1901) pp. 371-421. 



