28 



COMPENDIUM OF GENERAL BOTANY. 



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

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

 KRABBE 1 considerable growth in surface may be noticed in lamellse 

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

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

 dently are (ZIMMERMANN, KNY) formed in direct opposition to the 

 hydrostatic pressure of the cell ; therefore their growth cannot be 

 the result of expansion through hydrostatic pressure. 2 (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 growth ; 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 processes 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 KEINHARDT on the other, 

 the following statement in regard to surface- 

 growth of the cell- wall will hold good, and 

 wil1 not be contradictory to what has been 



said before - ^ ew la ^ ers are without doubt 



n -ff pl) rJpnnsifprl hv thp rmmnrrlial nfn'plp 

 J ien ( D J Tn ' P ri 



while surface growth is going on; the outer 

 and older layers are 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 S 

 investigations it is not demonstrable in hyphal fungi (Peziza). 



The following interesting observation will aid one in judging 

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

 growing cells (fungal hyphse) 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 



III. Eight-celled colony of Gloeo- 

 capsa alpina, Nag. (X 500. After 



1 Pringsheim's Jahrbucher, XVIII (1887). 



2 Supposition of the defenders of the apposition theory. 



3 Pringsheim's Jahrbilcher, XXIII (1892). 



