SECT, n PHYSIOLOGY 297 



VI. Reproduction 



The life of every plant is of limited duration. Death ensues, 

 sooner or later, and the decayed remains form a part of the surface 

 soil. All existing plants are descended from ancestral forms. A 

 spontaneous generation of new organisms from lifeless matter does 

 not, as far as experience teaches, take place, and all existing vegetable 

 life owes its existence to the capacity inherent in all organisms of 

 reproducing their kind. Reproduction is accordingly a vital power 

 which must be exercised by every existing plant species. 



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

 the production of new organisms a process of rejuvenation is con- 

 tinually being carried on. The descendants commence their develop- 

 ment at a stage long since passed over by the parents. 



The formation of independently existing offspring necessitates 

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

 bud by a tree is not distinguished as reproduction so long as the bud 

 remains in connection with the tree as a part of the whole. 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 a large fern. BP;SSEY 

 has estimated the number of seeds produced annually by a Poplar 

 tree at about 28 millions. 



REJUVENATION, SEPARATION, 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, indeed, essentially 

 based upon differences in the development of the reproductive organs 

 and in their functions. 



Numerous and varied as the processes of reproduction in the 

 vegetable kingdom are, they are in reality but modifications of two 

 different and distinct modes of reproduction. 



The simpler of these, or VEGETATIVE REPRODUCTION, consists in 



