i86 The Anatomy of Plants BOOKII 



by suggesting that there is no universally applicable method, 

 but that growth, both in surface and thickness, can be 

 brought about in both ways. 



Pfeffer showed that the stretching of the cell wall during 

 surface-growth depends to some extent on a softening of 

 its substance by the protoplasm. 



Since Pfeffer's work appeared, further contributions have 

 been made to the controversy which seem to justify his 

 suggestion. Correns in 1893 found that intercalation of 

 particles takes place in the walls of Gleocapsa and Apio- 

 cystis ; Cramer found an increase in the mass and volume 

 of the walls of Neomeris Kelleri in the absence of any 

 possibility of growth by apposition. In 1897 Kolkwitz 

 showed that rapid growth of the cell wall occurs in the 

 pith of certain stems, which are hardly stretched at all 

 during the period of the most active increase in size, con- 

 firming thus the observations of Pfeffer four years earlier, 

 that the growth of the walls of certain cells in the root 

 can continue after osmotic pressure in such cells has been 

 almost destroyed. Reinhardt carried out some observa- 

 tions on the growth of certain fungal hyphae in 1899, 

 which led to the same conclusion. Strasburger himself 

 accepted the view of different modes of growth of cell wall 

 in different cases in his work of 1898. 



Strasburger gradually modified his views after the publi- 

 cation of the Ban und Wachstum of 1882, in which his 

 hypothesis first appeared. In his Bau und Verrichtungen 

 der Leititngsbahnen (Jena, 1891), he admitted that the proto- 

 plasm of the cell may at times make its way into the wall 

 and become modified to form some of the products which 

 occur there, apart from the normal framework. He ad- 

 mitted that the cell wall is not formed at once and for all, 

 but that the protoplasm abutting on it exhibits a con- 

 spicuous power of modifying its constitution. He was thus 

 prepared even then to accept intussusception of a kind, 



