sect, ii PHYSIOLOGY 275 



with wild plants in the struggle for existence, and consequently would 

 soon die out were they not protected and multiplied by artificial means. 

 A great number of our cultivated plants belong to this class of artifici- 

 ally maintained plant forms. 



It is also evident from the very nature of reproduction that in the 

 production of new organisms a process of rejuvenation is continually 

 being carried on. 



The formation of independently existing offspring necessitates also 

 their separation from the parent plant. The formation of a new bud 

 by a tree would never be distinguished as reproduction so long as the 

 bud remained in connection with the tree as a part of its life. But if 

 the bud became separated from the tree and continued its existence as 

 an independent plant, that would constitute a form of reproduction, 

 and, in fact, this actually takes place in many plants. 



The conditions of the outer world make the still further demand 

 upon reproduction, that from it a multiplication of the species should 

 result. As the germs after separation from the mother plant do not 

 always find the conditions necessary for their development and so, for 

 the most part, perish, the extinction of the whole species would soon 

 result if a plant produced but a single germ. That in reproduction 

 care is taken for the multiplication of the individual in an almost 

 spendthrift manner, is shown by a consideration of the innumerable 

 spores produced by a single mushroom, or by the thousands of seeds 

 contained in the fruit capsule of an orchid. 



Separation, rejuvenation, and multiplication of the individual 

 are accordingly the essential requisites of reproduction. 



These requirements are fulfilled by plants in the most varied 

 manner. Each great division of the vegetable kingdom has adopted 

 its own special method ; and each family and genus, or even the 

 different species, are characterised by some peculiar feature of their 

 manner of reproduction. Systematic botany is so essentially based 

 upon the different development of the reproductive organs and their 

 functions, that it consists for the greater part of special descriptions of 

 the processes of reproduction in the vegetable kingdom. 



Numerous and varied as these processes are, they are in reality 

 but modifications of two different and distinct modes of reproduction. 



The simpler of these, or Vegetative Reproduction, consists in the 

 formation of cells or cell bodies which, after their separation from the 

 parent plant without undergoing any further change, either germinate 

 at once, or develop into new organisms after a period of rest. This 

 mode of reproduction, in which the growth and development of the 

 parent plant are directly continued, is also distinguished as MONO- 

 genetic, vegetative, or asexual reproduction. 



In Sexual Reproduction, the second of the two modes of propa- 

 gating vegetable life, two kinds of reproductive cells are first formed, but 

 neither is directly capable of further development, and both perish in 



