28 



COMPENDIUM OF GENERAL BOTANY. 



growtli in thickness as well as in surface, yet the following considera- 

 tions are opposed to a surface growth by apposition. According to 

 Krabbe ^ considerable growth in surface may be noticed in lamellae 

 of various bast cells which are not in direct contact with the cell- 

 plasm. Further, there may occur cell-ivall foldings which evi- 

 dently are (Zimmermann, Knt) formed in direct opposition to the 

 hydrostatic pressure of the cell ; therefore their growth cannot be 

 the result of expansion through hydrostatic pressure.'' (This will 

 again be referred to in the chapter on the physiology of growth.) 



The very frequent spiral arrangement of the molecules of cylin- 

 drical cells is also evidence in favor of the theory of internal pro- 

 cesses of growtli ; this apparent twisting of 

 the cell upon its axis is more easily explained 

 by growth processes within the interior of 

 the cell-wall than by jirocesses of apposition- 

 Phenomena of tension which become mani- 

 fest when starch-grains are partially cut also 

 point to internal differentiations. 



According to the investigations of 

 ScHMiTz, Strasburger, and Noll on the 

 one hand, and Reinhardt on the other, 

 the following statement in regard to surface- 

 growth of the cell-wall will hold good, and 

 will not be contradictory to what has been 

 icunda Ks. iL Two '- celled gaij beforc. Ncw lavcrs are without doubt 



olony or Glieoaipsa alpina, I^afr. •/ 



"ps?c!K;«r/;Nkr'&a AfT;; often deposited by the primordial utricle 

 Pa3ation"approJinmtei7' c^^^^^^ whilc surfacc growth isgoingou; the outer 

 rect at the periphery.) ^^^^ ^j^^^. j^^^^^.^ ^^^ thereby passively ex- 



panded and ruptured. These layers very probably grow in surface by 

 intercalation (intussusception). Such formation of new lamellae must 

 not of necessity always take place. According to Reinhardt's ' 

 investigations it is not demonstrable in hyphal fungi {Pezisa). 



The following interesting observation will aid one in judging 

 the "theory of expansion " more critically. The advancing tips of 

 growing cells (fungal hyphae) were observed directly. By the aid 

 of adhering granules it was noticed that the increase in surface was 

 at a maximum at the place of greatest curvature, and extended only 



OIL 



Fig. 12. 



I. Single cell of Glofocapsa ru- 



b 

 colo 



' Pringsheim's Jahiblicher, XVIII (1887). 



* Supposition of the defenders of the apposition theory. 



3 Pringsheim's Jahrbilcher, XXIII (1892). 



