INTRODUCTION 3 



under two heads: nutrition and reproduction. This means 

 that every plant must care for two things: (1) the support of 

 its own body (nutrition) and (2) the production of other 

 plants like itself (reproduction). To the great work of 

 nutrition many kinds of work contribute, and the same is 

 true of reproduction. In a complex plant, therefore, there 

 are nutritive organs and reproductive organs; and this 

 means that there are certain organs which specially con- 

 tribute to the work of nutrition, and others which are 

 specially concerned with the work of reproduction. It 

 must not be supposed that an organ is necessarily limited 

 to one kind of work. Its form and structure fit it for a 

 particular kind of work, which may be called its specialty; 

 but it is not excluded from other kinds of work, just as 

 a man who is specially trained to be a carpenter may do 

 other things also. 



6. Life-relations. In all of its work a plant is very de- 

 pendent upon its surroundings. For example, it must 

 receive material from the outside and get rid of waste 

 material. Therefore, organs must establish certain definite 

 relations with things outside of themselves before they can 

 work effectively; and these necessary relations are known 

 as life-relations. For example, green leaves are definitely 

 related to light they cannot do their peculiar work 

 without it; many roots must be related to the soil; certain 

 plants are related to abundant water; some plants are re- 

 lated to other plants, as parasites, etc. It is evident that a 

 plant with several organs may hold a great variety of life- 

 relations, and it is a very complex problem for such a plant 

 to adjust all of its parts properly to their most effective 

 relations. It must not be supposed that even a single organ 

 holds a perfectly simple life-relation, for it is affected by a 

 great variety of things. For example, a root is affected by 

 gravity, moisture, soil material, contact, etc. Each organ, 

 therefore, must become adjusted to a complex set of rela- 



