4. Photo-sytitax, or those processes through which, under the influ- 

 ence of the light, the crude food materials derived from soil 

 and air are transformed into substances suited to the needs 

 of the plant. 

 While for the purposes of this leaflet, only one of these uses, that 

 of transpiration, will be considered, the others have been given to 

 show how essential the light relation is to the foliage leaf if it ac- 

 complish its assigned work. The foliage leaf then is not merely an 

 ornamental appendage to the plant, its various peculiarities being 

 considered as the result of chance, but a working organ intimately 

 concerned with the most important duties in the individual life of the 

 plant. 



Let us now examine some of the ways in which this light relation is 

 secured. One of the forms, often seen, especially in the early spring, 

 is that known as the "rosette" arrangement. The foliage leaves are 

 apparently arranged radially, lying flat upon the ground, and in the 

 absence of the stem, seeming at first glance quite unlike organs for 

 light relation. Common plants with this arrangment are the mullein 

 and plantain. If the leaves in this arrangement are without leaf stalks, 

 it will be found that in almost every case they are broader at the apex 

 than at the base, a form which in definitional botanies is known as 

 spatulate. The successive circles of leaves as they arise from the center 

 are progressively shorter, the broader portions at the apex fitting into 

 the spaces left between the narrowed bases of the leaves of the preced- 

 ing circle. If the whole rosette be looked at from above it will be seen 

 that scarcely any portion of the lower leaves is shaded by those above, 

 each leaf, by its peculiar form and the regularly diminishing size of 

 the leaves of succeeding circles, being brought into the most perfect 

 light condition. 



In the case of the plaintain, where leaf-stalks are present, the same 

 condition is brought about by the progressive shortening of the leaf- 

 stalk from the lower to the upper circles of leaves. It is very evident 

 then that the "rosette" arrangement is a device for securing the light 

 relation on the part of plants with reduced stems. 



Material fob Illust ration : 



Common plantain, earlier leaves of mullein, shepherd's purse, dandelion 



Taking the cases where leaves are found upon a well developed 

 stem, the most casual examination will show device after device for 

 securing proper light relations. So evident are they, that they need 

 not be mentioned in detail, almost every species of plant furnishing its 

 own solution to the problem. If an ordinary erect stem is looked at 



