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. Itis 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- 
