1886-87.] in regard to the Vegetable Cell-Wall. 45 



to explain growth in surface on the " apposition " theory, but 

 Strasburger* himself admits that when the pollen grain is 

 germinating the cell is not turgid, but is, in fact, largely empty. 

 Another instance occurs in the development of the air-balloons 

 in the pine pollen. It is found here that, after the intine has 

 been forrmed, a swelling of the extine takes place by which the 

 hemispherical spaces between the extine and intine are pro- 

 duced. Though Tschistiakofft states that a ceitain amount 

 of protoplasm is left between the' two coats, this protoplasm 

 is, according to him, dead, and can scarcely be supposed able 

 to produce the growth of the extme. Another interesting- 

 case is found, according to Krabbe,| in the development of a 

 vessel from an ordinary cambium cell. The walls of the 

 vessel, which have very different cross sections, do not 

 specially bulge into the walls of the neighbouring cells, 

 hence Krabbe concludes that the pecuHar growth is not pro- 

 duced by turgidity, but by an " active growth of the mem- 

 brane," or "a specific activity of the cell membranes in contact 

 with the protoplasm." Dr Macfarlane has observed in the 

 first stage of conjugation of two Spirogyra cells, that the pro- 

 tuberances are wholly formed by the cell- wall, the protoplasm 

 forming no projection of corresponding size. This is, therefore, 

 a case of independent growth due to the cell- wall alone. Stras- 

 burger^ has studied the development of certain prominences 

 on the hairs of Marsilea Ernesti ; he finds that these are due 

 to a bulging out of the protoplasm, and suggests that the 

 protoplasm produces a local extensibility of the cell-wall at 

 the place where this occurs. But he also points out that, in 

 the case of similar prominences on the hairs of Coleus, sp., 

 this bulging does not occur until an inner layer has been 

 formed below the place where bulging of the outer layer 

 afterwards occurs. Both these cases seem to me most 

 simply explained as cases of growth of the cell-wall.|| 



Schenck^ gives some instances of a smiilar kind, viz., the 

 prominences on the hairs of Deutzia scahra, folds of the epi- 

 dermis on the petals of Narcissus Tazetta, and in another paper 



* Strasburger, loc. ciL, pp. 199, 200. 



t Tschistiakoff, Botan. Zcitung, 1875, p. 97. 



+ Krabbe, Das Glcitciidc Wachathimi d. Zellhaute, Berlin, 1886; see Bot. 

 Geiitralblatt, Bd. xxix., 1887, p. 3. § Loc. ciL, pp. 146, 181. 



II Strasburger explains the case of Coleus as " Volumenzunahme " through 

 cuticularisation. IT Schenck, Bot. Zcitung, 1884, p. 733. 



