112 RECORD OF CURRENT RESEARCHES RELATING TO 



The method of production of these nuclei is by " division," i. e. a 

 process of several stages, hitherto claimed for the wm nuclear cells 

 alone ; but he has observed it in the case of the three first-mentioned 

 plants in the liber-cells, and in the two second in the laticiferous 

 cells as well : the division just stops short of the formation of septa ; 

 the nuclei in one cell, sometimes numbering thirty, generally divide 

 simultaneously. 



The process of " free cell-formation " occurs in the same manner, 

 according to Strasburger, but proceeds to the aggregation of proto- 

 plasm round the dififerent nuclei, and thus forms new cells. 



These discoveries tend to exalt the importance of the nucleus in 

 these processes at the expense of that of the protoplasm. 



Contraction of Cells through Absorption of Water-* — The con- 

 traction of cells by the loss of water is a well-known i^henomenon of 

 vegetable physiology ; not so, however, that of contraction by absorp- 

 tion of water, which, however, according to H. de Vries, is very 

 common in roots. 



It has long been observed that the winter buds of many biennial 

 plants, which expose their cotyledons and jilumule above the surface 

 of the soil in spring, retreat entirely beneath the surface in winter. 

 This can obviously only take place from a contraction in length 

 of the root. By means of horizontal marks, a contraction was 

 measured in roots of red clover and beet j^lanted in water or wet soil, 

 to the extent of 10 to 15, or even in some cases of 20 to 25 per cent. 

 The greater part of the contraction takes place during the first part of 

 tlie time, a corresponding increase in thickness being manifested at 

 the same time. This change in the form of the cells is most con- 

 spicuous in the cambial tissue of the root, decreasing with the increase 

 in age of the cells, both in the wood and in the bark. The contj'actile 

 element is, therefore, the parenchymatous cells, the rest of the cells 

 remaining passive, and even offering considerable resistance. 



The contraction on absorj)tion of water is a phenomenon of 

 turgidity ; and contraction from increase of turgidity can only result 

 from an unequal extensibility of the cell-walls in different directions. 

 The very common phenomenon of transverse wrinkles on roots is a 

 result of this contraction. 



Suberization of the Membrane of Secretion-reservoirs.t— The 



structure of the walls of reservoirs for special secretions has been made 

 a subject of investigation by E. Zacharias, who finds that the trans- 

 formation into a corky substance is a very common phenomenon. 

 This was especially found to be the case in all the reservoirs exa- 

 mined which contained a colourless or bright yellow volatile oil 

 soluble in alcohol ; while reservoirs with suberizcd walls containing 

 mucilage or raphidcs were observed only in the genera Aloe, Mesem- 

 hryanthemiim, and Ilohenhergia ; suberization had not taken place in 

 those of Aletris fragrans, Orchis, and Cactacese. In their earliest 

 stages, oil, mucilage, and raphidcs were invariably found in all the 

 receptacles. Only in Batatas edidis was protoplasm with a nucleus 



* ' Bot. Zeit.,' xxxvii. (1879) p. 649. f Ibid., pp. 617, 633. 



