CHAP, i.] PLANT ARCHITECTURE. 1 



development of the special senses ; but it must be re- 

 membered that many of the lower groups of organisms 

 universally admitted to belong to the Animal Kingdom 

 are entirely destitute of every structural trace of a nervous 

 system. A third character of a negative nature is the 

 absence of differentiated cell- walls. 



The primitive types of the Vegetable Kingdom, if not 

 actually derived by modification from certain members 

 usually included in the Protozoa, are certainly most 

 nearly allied and often almost indistinguishable from the 

 latter, and the first indication of a break away from such 

 primordial types consisted in the development of a green 

 colouring substance called chlorophyll, which enabled 

 the organism to feed on inorganic matter ; and the 

 power of feeding on inorganic food taken into the body of 

 the plant in a gaseous form or in solution is the most 

 important characteristic of plant life, and it will be shown 

 that the adoption of this new method of obtaining food 

 has been the direct or indirect cause of the very great 

 variety of form and structure presented by the vegeta- 

 tive parts of plants. A second important character is 

 the presence of highly differentiated permanent cell-walls. 

 No trace of nerve tissue is present in any member of 

 the Vegetable Kingdom, nevertheless it will be shown 

 that certain movements and responsions to external 

 agencies manifested by some plants agree in important 

 points with similar movements manifested by members 

 of the Animal Kingdom, and which in the latter are con- 

 sidered as being the outcome of nervous excitation. 



The conception as to the origin of plants and animals 

 entertained at the present day differs from the older idea 

 of so-called " special creation " in the belief, which on 



