478 SUMMARY OF CDURENT IlKSKAUCUKS RELATING TO 



Bievo-tul cs wliicli can produce alljuniinous suLstiinccs, since they still 

 posscps a mu'lcus whicli is wanting in tlic mature tubes. He agrees 

 with Strasbiirger in regarding the nucleus as an important organ in 

 the formation of albuminoids. 



Development of the Sclerenchymatous Fibres of the Oleander.* 

 — ]M. A. Faniintzin has paid attention to tlic develoiiment of these 

 structures, especially with the view of determining whether it is best 

 explained on the theory of development by apposition or by intus- 

 susception. In the first two internodes, the membrane of these fibres 

 is thin, and composed only of the jjrimary layer. In the third inter- 

 node secondary layers are for the first time formed, in some cases two 

 secondary layers, and in subsequent internodes several ; the peculiar 

 strii'tion makes its appearance usually only in the fifth internode, in 

 the form of spiral bands, which in the sixth and seventh internodes 

 become split into a large number of very narrow strife. The general 

 conclusions at which the aiithor has arrived are: — (1) Each thicken- 

 ing layer increases in thickness by a2)position, new molecules of cellu- 

 lose being formed on the inner surface of the layer ; (2) the lamellaB 

 are formed by the splitting of the layers ; (8) it must still be regarded 

 as undecided whether each secondary layer is formed by the splitting 

 of an older layer, or by apposition. 



Growth of the Thickening-ring in Exogens.f — Dr. G. Krabbe 

 maintains that Do Vries's ex2jeriments on this subject are as easily 

 explained on the theory of a gradual decrease of the pressure of tho 

 cambium as on that of an increase of the tension of the bark. 



In Coniferae (Pinus Strohus) Krabbe found the radial tension of 

 the bark to be nearly the same in autumn as in spring ; while in 

 Angiosperms there is usually a small decrease in tlie autumn, though 

 not to a greater extent than one-quarter of an atmosphere. The greater 

 part of tangential tension falls on the comjiaratively thin periderm. 



The author describes an experimental method by which he proves 

 the truth of tho usual formula for expressing the radial pressure, viz. — 



T> J. 1 tangential tension 



Kadial pressure = — ° , . 



radius 



In both Conifers and Dicotyledons every radial row of cells in the 

 thickening-ring results from the repeated division of a single initial 

 mother-cell ; while in the meristcm of the medullary rays the cells 

 immediately derived from this initial cell become, without any pre- 

 vious division, the cells of the medullary rays of the phloem or xylem. 

 During the development of the annual ring the author distinguishes, 

 in the growing layer of tissue, two zones : that of cell-division or 

 the thickening-ring, and that of cell-elongation or the zone of the 

 young wood-cells. 



Internal Cambium Ring in Gelsemium sempervirens.J — Dr. J. 

 T. Rothrock calls attention to the internal cambium-ring in the stem 



* Bull. Acad. Imp. Sci. St. Petersburg, xxix. (1884) pp. 416-22 (1 pi.), 

 t Abh. K. Akad. WisB. Berlin, June 12, 1884. -See B.-t. Cmtralhl., xxi. 

 (1885) p. 38. 



: Prof. Acad. Nat. Sci. Philad., 1885. pp. 22 3. 



