214 A LESSON ON BUTTERCUPS. 



leaves acting more or less similarly in doing the work of 

 roots and leaves both. 



In the type growing in sluggish or stagnant water, a 

 second type of leaf occurs, viz. the floating leaves. Here 

 the leaf stalk is long and slender, the blade orbicular and 

 lobed, the under side is covered with short hairs, the upper 

 side is smooth. There are no stomata on the under side, 

 but on the upper they are very numerous. 



The most noteworthy adaptation here is, of course, the 

 situation of the stomata. These leaves function as ordi- 

 nary foliage leaves and transpiration is possible only into 

 the atmosphere, hence the stomata occur only on the sur- 

 face which is above water. It is an interesting fact that 

 i ntermediate types of plant exist showing more or fewer of 

 either type of leaf depending on situation as regards 

 amount of water. The plant sometimes grows in marshy 

 places when all the leaves are of the aerial type. 



The flowers, which have smooth cylindrical stalks, are 

 borne above the water. The petals are whitish, but other- 

 wise there is nothing distinctive. Whilst we note much 

 modification of all of the vegetative parts of the plant in 

 relation to changing environment, we must contrast with 

 this the relative constancy of the floral parts. 



These two types have been considered in some detail, 

 not only that these lessons may be repeated along with the 

 pupils, but also that the beginner may be helped to grasp 

 the principle of adaptation to environment (science of 

 Ecology). If he cares to follow up the subject as a mat- 

 ter of training which will help in interpretation, he should 

 take the opportunity to describe in detail other species of 

 buttercup, of which there are several, noting carefully the 

 general situation in which the species occurs and its time 

 of appearing. 



If he makes use of a compound microscope, and cuts 

 thin sections of the various parts with an ordinary razor, 

 and takes the trouble to draw them, the work will be cor- 

 respondingly more valuable. For it will have been noted 

 already how much a study of internal structure reveals 

 important adaptive peculiarities. 



