STRUCTURE OF THE PLANT 



15 



green foliage of plants. Having produced such a leaf 

 the plant seems to have reached the beaten track and 

 produces one leaf after another, modelling them as it 

 were according to the same pattern, casting them, so 

 to speak, in the same mould. But the leaves are not 

 the only product of a growing plant ; at a certain age 

 it produces other organs such as flowers and fruit. 

 As a rule the transformation of leaves into quite distinct 

 flower organs hap- 

 pens suddenly; but 

 cases are frequent 

 in which the ap- 

 pearance of the 

 flower is anticipated 

 by changes revealed 

 in the upper leaves. 

 Let us study the 

 well-known garden 

 peony. Everybody 

 knows its leaves (fig. 6). Starting from the lowest and 

 passing up the stem towards the flower we notice that 

 the shape of the leaf changes until it becomes at last 

 almost unrecognisable. At first the whole leaf consists 

 of eleven or nine leaflets distributed in threes. At a 

 certain point we have only three leaflets ; in the interval 

 between these two kinds of leaves we are also likely to 

 find such as have seven and five leaflets. In the end 

 the whole leaf consists of only a single leaflet (fig. 7, left) . 

 The process is the converse of that noticed in the ash. 

 There the shape of the leaf became gradually more 

 complicated, whereas here it becomes less so, passing 

 through the same stages but in the reverse order. 

 So far the simple leaflet has entirely resembled the upper 

 part of the whole leaf, but gradually it also changes its 

 appearance : its short petiole broadens into a flat 

 scale, while the lamina continually decreases until it 

 becomes a small, green, tongue-shaped object on the top 



Fig. 5. 



