254 SUMMARY OF CURRENT RESEARCHES RELATING TO 



at the most external part of each bundle, and the differentiation pro- 

 ceeds from without inwards. 



In Dicotyledons the transformation from the arrangement of the 

 bundles in the stem to that of the root generally takes place in the 

 tigellum ; while in Monocotyledons the root arrangement of the 

 bundles continues nearly as far as the point of insertion of the coty- 

 ledons in Phcenix dactylifera, or of the scutellum in Zea Mais. 



Suberin of the Cork-oak.* — A. Meyer gives the general results of 

 some investigations made by Kligler as to the nature of the suberin of 

 Quercus suber. The micro-chemical reactions of suberin show that it is 

 nearly allied to the fatty oils. Its molecules are so closely associated 

 with those of cellulose, that boiling chloroform, while extracting the 

 whole of the crjstallizable cerin, removes only about 25 per cent, of 

 the suberin. It is, however, completely extracted by treating first with 

 chloroform and alcohol and then with an alcoholic potash-ley. Kiigler 

 regards it as a fatty oil, composed chiefly of stearin (Ci8H350^)3C3H5 and 

 the glycerin-base of a new acid, phellonic acid C20H42O3, with melting- 

 point 96° 0. Forty per cent, of the mixture of these acids, and 2 * 5 per 

 cent, glycerin was obtained from cork. 



Suherin is therefore closely allied to the tallows, and especially to 

 Japan tallow, which, besides palmitin, contains the base of an acid 

 with high melting-point 95'' C, obtained from the parenchyma-cells of 

 Ithus succedanea, a substance apparently identical with that which 

 causes the suber ization of the cell-walls. 



Influence of Pressure on the Growth and Structure of Bark.j — 



A. Gehmacher finds that pressure exercises a considerable influence 

 on the growth of bark, the separate elements being altered as definitely 

 as those of the wood. 



As regards cork, the greater the pressure the fewer cork-cells are 

 formed, and the less the pressure the more numerous are they. The 

 radial diameter of the cells is also affected by the pressure. 



The cells of the primary cortical parenchyma undergo a similar 

 change ; but they appear to be compressed not only radially, but also 

 laterally, becoming more or less angular towards those cells which 

 were formed under less tension and have a more nearly globular form. 

 The intercellular spaces disappear entirely with increased pressure, 

 increasing perceptibly in size with its decrease. The sclerenchyma- 

 tous elements are least affected by change of pressure. The bast-fibres 

 increase considerably in number with diminution of pressure ; when the 

 pressure is very great very few bast-fibres or none at all are formed. 

 Both the wood-fibres and bast-fibres increase in size with diminished 

 pressure. 



Relation of Transpiration to Internal Processes of Growth.| — 



According to P. Sorauer, transpiration results from two sources, viz. 

 the water derived from processes of oxidation within the plant, and 



* Ber. Deutsch. Bot. Gesell., i. (1883); Getieralvers. in Freiburg, xxix.-xxx. 

 t SB. K. Akad. Wiss. Wien, Ixxxviii. (1883) (1 pL). 



X Forsch. aus d. Geb. der Agriculturphysik, vi. (1883) p. 79. See Natur- 

 forscher, xvi. (1883) p. 470. 



