34 A History of Botany, 1860-1900 



mission of the characters which an organism inherits from 

 its parent. He held this idioplasm to be the seat of the 

 potentiality alluded to, and generation by generation to 

 make advances in complexity. He admitted that this 

 plasticity can be moulded more or less by external con- 

 ditions and that if these act in a particular direction for 

 a lengthened period considerable adaptive modification of 

 form and structure may result. He differed from Darwin 

 in particular by denying that all organization is essentially 

 adaptive, laying stress on the potentiality of spontaneous 

 evolution of the idioplasm. 



A great Algologist passed away in 1894 in the person of 

 Pringsheim, who made a special study of these organisms 

 from 1855 onwards. His \vork was not, however, confined 

 to them ; in his later years he gave a good deal of attention 

 to vegetable physiology, and in particular to the nutritive 

 processes of the green plant. In this department he was 

 much less successful, for his name is associated in particular 

 with his theory of hypochlorin as one of the early products 

 of chlorophyll activity, and of the famous hypothesis of the 

 screening action of chlorophyll in carbon appropriation 

 neither of which stood the test of examination. 



A good deal of Pringsheim's work falls into our period ; 

 his studies prior to 1860 had, however, earned for him a very 

 high reputation. He investigated the Coleochetaceae in 

 1858 and discovered the much-discussed alternation of 

 generations in the group. He showed in the same year 

 that in fertilization or conjugation an actual fusion of the 

 sexual cells takes place, and not as Thuret had said, a mere 

 dynamical reaction. 



He investigated various groups of Algae during the 

 next ten years, and contributed many important dis- 

 coveries to science. One of his most interesting publica- 

 tions was his memoir on the morphological differentiation of 

 the Sphacelariae, published in 1871. On other groups the 



