1886-87.] in regard to the Vegetable Cell-Wall. 43 



development. Strasburger* admits that cutinisation and such 

 prominences of ciitin are often developed on walls already 

 highly thickened. As an explanation, he states that cuticula- 

 risation is always connected with increase of volume.t This 

 requires proof, however, and he himself states that the cuticle 

 is formed from the union of the distended walls of the mother- 

 cells of numerous generations,| which seems to me rather 

 against the previous statement. 



With regard to lignification, Russow § states in a recent 

 paper that the walls of the wood cells of Coniferse grow by 

 intussusception. Strasburger|| affirms that they are formed 

 by apposition throughout ; he confesses, however, that lignifi- 

 cation does not occur till after every trace of protoplasm has 

 disappeared from, the cell, and this seems to me hard to 

 explain on this view. As WeisnerU points out, his theory 

 would explain all such changes. This is quite true, for we 

 cannot say what protoplasm might not do. 



It appears" probable that, in the majority of cases, this 

 intramural protoplasm does not grow. One might perhaps 

 consider that, instead of the cohesion of the molecules of a 

 stretched lamella being overcome (cf. Schmitz and Stras- 

 burger) the protoplasmic strings connecting the dermatosomes 

 are either stretched or grow (though Wiesner H apparently 

 does not hold this view). 



There is certainly no doubt that in the majority 

 of cases new lamellae are formed from the protoplasm 

 of the cell, and not that within the wall. As examples 

 may be mentioned the cellulose thickenings on injured 

 threads of Vaucheria (Schaarschmidt),"^* and the episporium 

 of Peronospora ovum formed from the epiplasma (De Bary).tt 

 Strasburger, while satisfactorily explaining doubtful cases 

 like the shell of the Brazil nut {cf. Millardet),^ gives an 

 immense number of cases of this kind, e.g., elater coat of 

 Equisetum spores, pollen of Gaura hicnnis and Scahiosa 

 caucasica. §§ Moreover, it is possible actually to see the for- 

 mation of the cell-wall. Dr Macfarlane informs me that at 

 a certain stage in the development of the cell-wall of Spiro- 



* Strasburger, loc. cit., p. 99. t Loc. cit., p. 199. + Loc. cit., p. 192. 

 § Russow, Newen Dorpatschen ZeAtimg, 1881; see Strasburger, Zoc. cit., p. 38. 

 II Loc. cit. H Loc. cit.; see also Bot. Centralb., Bd. xv., 1886, p. 353. 



** Loc. cit, t+ Loc. cit., p. 145. 



tt Millardet, Ann. d. Sci. Nat., 1866, p. 304. 

 §§ Loc. cit., pp. 100, 121, 129. 



