202 



A TEXTBOOK OF BOTANY [Ch. IV, 12 



for the usual color substance, of which the formation is 

 inhibited by some accident. We sometimes find the oppo- 

 site phenomenon, where the 

 floral color is thrown into 

 leaves, as happens with some 

 Tulips, in which the upper- 

 most leaf of the flower-stalk 

 takes the color of the flower. 

 Genuine reversions no doubt 

 do occur ; and perhaps we 

 have a case in the occasional 

 appearance of leaves upon the 

 smooth sides of Apples and 

 Cucumbers, this part of the 

 fruit being morphologically 

 stem. Sometimes Potatoes 

 appear above groimd in the 

 axils of the leaves, evidently 

 because food material destined 

 for the underground tubers 

 becomes chverted into axillary 

 buds. 



There can be little doubt that with increasing knowledge 

 we shall learn to control such substitutions, and various other 

 stimuli which produce special growths upon plants. Thus the 

 horticulture of the future will surely include some practice 

 whereby palatable and nutritious growths, on the analogy of 

 aerial tubers and galls, will be produced at will ujion the 

 leaves or stems of plants. 



Several forms of monstrosities are distinctive of leaves. 

 Rather common is the formation of a cornucopia-like pitcher, 

 instead of a flat blade, as happens in Pelargoniums, Cabliage, 

 and others (Fig. 1.51). Here the bases of the leaf blade seem 

 to unite or graft together over the petiole at an early stage, 

 and remain united during the subsequent growth. The 

 case has an interest in showing one way in which pitchers 



Fig. 1.50. — Proliferou.s Rose 

 (From Masters, Vegetable Tera- 

 tology.) 



