

INTRODUCTION 



ORGANISMS are customarily distinguished as animals and plants and 

 a corresponding division of Biology, which treats of living beings 

 generally, is made into the sciences of Zoology and Botany. 



The green, attached, flowering, and fruiting organisms are dis- 

 tinguished as plants in contrast to animals, which are usually capable 

 of free movements and seek, capture, and devour their food. Easy as 

 it appears on a superficial acquaintance to draw the boundary between 

 the vegetable and animal kingdoms, it is really very difficult. In the 

 case of those very simply constructed organisms with little external or 

 internal differentiation, which are usually regarded as lowest in the 

 scale, all distinguishing characteristics may fail us. The following 

 important properties are in fact common to both animals and plants : 



1. Plants and animals both consist of one or many microscopically 

 small cells, which increase in number by a process of division. They 

 have thus a FUNDAMENTALLY SIMILAR INTERNAL STRUCTURE. 



2. Plants and animals are living beings and AGREE IN THEIR MOST 

 IMPORTANT VITAL PROCESSES. The processes of nutrition and of 

 reproduction, of growth and of development, are, broadly considered, 

 essentially similar in animals and plants. A plant also respires with 

 the production of heat, and exhibits powers of movement and 

 irritability of various kinds. 



3. This profound agreement in the manifestations of life in plants 

 and animals becomes less surprising when it is realised that THE 



LIFE OF BOTH IS ASSOCIATED WITH A VERY SIMILAR UNDERLYING 

 SUBSTANCE, THE PROTOPLASM OF THE CELLS. 



These and many other facts indicate that plants are really related 

 among themselves and to the animals. This assumption of a GENETIC 

 RELATIONSHIP finds its expression in the THEORY OF DESCENT which 

 may be regarded as the fundamental biological theory. The idea of 

 a gradual evolution of higher organisms from lower was familiar to 

 the Greek philosophers, but a scientific basis was first given to this 

 hypothesis in the last century. It was especially through the work of 

 CHARLES DARWIN (*), who accumulated evidence for a reconsideration 



