SUMMARY 139 



In anatomy the investigations, more especially, of 

 Schleiden, Von Mohl, and Naegeli, had led to the recogni- 

 tion of the cell as the fundamental unit in plant construc- 

 tion, and protoplasm as the physical basis of all plant 

 activities. It had been established that all the varied 

 types of cell, fibre, and vessel that went to the formation 

 of the different organs were derived from homogeneous 

 primary cells at growing points at the ends of roots and 

 shoots, or from layers or strands of similar embryonic 

 cells interpolated between permanent tissues, but the 

 knowledge that had been acquired of the mode of differen- 

 tiation of the permanent tissue elements from the initial 

 embryonic cells, and the relationship of the different 

 types of tissues to each other, was still very fragmentary. 

 What was as yet awanting was the vivifying influence of 

 the conception of physiological division of labour, and 

 that conception was necessarily bound up with the idea 

 of adaptation of structure to function. 



In physiology also matters were in a backward state ; 

 no physiologist of any particular note had succeeded 

 Dutrochet. Liebig and Boussingault had certainly done 

 much to clear up the question of the relationship of the 

 plant to the soil, more especially by upsetting the humus 

 theory of nutrition, and by determining the true source 

 of nitrogen, but both these men were chemists rather 

 than botanists. The problems of the ascent of sap, as 

 also of the precise function of chlorophyll in nutrition, were 

 still unsolved, and botanists were not even yet perfectly 

 clear as to the universal occurrence of respiration in plants. 



That all plants, save the very lowest, possessed 

 sexuality had just been realised, although in many 

 groups the reproductive organs were still unknown, and 

 it was only when the universal occurrence of protoplasm 

 in all living cells had been accepted as a fact, and when 

 the peculiar properties of that substance began to be 

 appreciated, that the physiology of sensitivity attracted 

 attention. 



