ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 261 



to the naked eye in thin sections of stems of Phaseolus multifloras that 

 are allowed to lie for thirty-six or forty-eight hours in a horizontal posi- 

 tion ; a very great thickening of the cell-walls having taken place on 

 the upper side, exposed to the irritation of direct sunlight in the whole 

 of the cortical parenchyma, including the epidermal cells. 



The author believes that these observations will throw great light 

 on certain phenomena at present difficult of explanation, such as latent 

 irritation and the secondary action. 



Irritability of the Stamens of Echinocactus.* — Mr. T. Meehan 

 notes the great irritability of the stamens of Echinocactus ottonis, a 

 phenomenon already recorded in many species of Opuntia and allied 

 genera. 



(4) Chemical Changes (including Respiration and Fermentation). 



Sources of the Nitrogen of Vegetation.f — Sir J. B. Lawes and 

 Prof. J. H. Gilbert in this paper discuss the present position of the 

 question of the sources of the nitrogen of vegetation, and also indicate 

 some new lines of investigation which they are following up. In earlier 

 papers, the authors had concluded that, excepting the small amount of 

 combined nitrogen annually coming down in rain, and the minor 

 aqueous deposits from the atmosphere, the source of the nitrogen of our 

 crops was substantially the stores within the soil and subsoil, whether 

 derived from previous accumulations, or from recent supplies by manure. 

 More recently it has been shown that the amount of nitrogen as nitric 

 acid in the soil was much less after the growth of a crop than under 

 comparable conditions without a crop. After giving the details of 

 numerous experiments performed by themselves and others, the authors 

 conclude by stating that whether or not the lower organisms may 

 be proved to have the power of bringing free nitrogen into combination, 

 it at any rate would not be inconsistent with well-established facts, 

 were it found that the lower serve the higher by bringing into an avail- 

 able condition the large stores of combined nitrogen already existing, 

 but in a comparatively inert state, in our soils and subsoils. 



B. CRYPTOGAMIA. 



Cryptogamia Vascularia. 



Conversion of Fertile into Sterile Fronds.f— Herr K. Goebel has 

 succeeded in converting the fertile sporophylls of Onoclea Struthiopteris 

 into barren green fronds, or rather in hindering the metamorphosis of 

 the latter into the former. This fern is distinguished by having three 

 distinct kinds of leaf, the fertile fronds, the barren fronds, and " cata- 

 phyllary leaves " which appear not only on the stolons, but also as bud- 

 scales inclosing the hibernating terminal bud. These are all modifications 

 of ordinary foliage leaves. The barren and fertile fronds differ from one 

 another in many important points of structure, as well as in the time 

 of their appearance, the former unfolding at the commencement, the 

 latter at the close of the period of vegetation. If at the end of June all 

 the barren fronds are removed, the fronds which subsequently unfold will 

 display all kinds of transitional stages between the two forms, their 



* Proc. Acad. Sci. Philad., 1887, p. 332. 



t Proc. Roy. Soc, xliii. (1887) pp. 108-16. 



% Ber. Deutsch. Bot. Gescll. (Gen.-Vcrsaniml. Heft), v. (1887) pp. lxix.-lxxiv. 



