General Introduction 15 



plasmic vesicle in this case forms the subsequent lining 

 of the young cells, and constitutes the " primordial utricle " 

 of von Mohl.' . . . ' In some cases no nucleus can be 

 detected in a cell previous to the formation of other cells 

 free in its cavity ; hence it is quite clear that the presence 

 of the nucleus cannot be regarded as essential, but that 

 the separation of a portion of the protoplasm from the 

 general mass must be capable of acting as one, and thus 

 to cover itself with a membrane and form a cell.' Hen- 

 frey's textbook contained a very similar account, but 

 ignored the nucleus altogether. 



It is hardly necessary to go into further details ; it is 

 only too clear that the need for new investigations was 

 pressing, and that especially new points of view and new 

 lines of research were imperatively required. 



The state of knowledge of physiology was still less 

 satisfactory— indeed it may almost be said that vegetable 

 physiology as a science had not yet come into existence. Since 

 the early researches of Senebier, Ingenhousz and de Saussure 

 no physiologist of eminence save Dutrochet had appeared. 

 Liebig had done great service in disposing of the ' humus ' 

 theory of nutrition, but the confusion he introduced into 

 the consideration of the important question of respiration 

 can only be called deplorable. Boussingault, like Liebig 

 an agricultural chemist rather than a botanist, had made 

 important investigations into the same range of problems, 

 connected with the supply of nitrogen to the plant. But 

 on the whole little progress had been made ; it is indeed 

 doubtful whether knowledge had not gone backward rather 

 than forward during the two decades prior to i860. 



The absorption and transport of water, the relation 

 which it bears towards the problems of nutrition, the 

 nature and meaning of the gaseous interchanges between 

 the plant and the atmosphere, the meaning of the presence 

 of chlorophyll— all problems of the highest importance— 



