RELATION TO SEXUAL T»l FKKRENTTATION. 47 



of very abriij)t and very extensive {'han<i;es of cliaracters. After 

 formin<x, it may be, several kinds of vep;etative internodes, the young 

 plant be<z;ins suddenly to make floral or reproductive internodes, each 

 kind of internode involvin*:; a ])ractically complete chani:;e of charac- 

 ters. The idea that plants coidd produce the slight changes of char- 

 acters shown in bud mutations has seemed highly improbable to 

 those who have not witnessed such changes, thougli more exten- 

 sive changes regularly take place in the development of each plant. 



Beginning with the formation of cotyledons or seed leaves, the 

 plumule of the embryo has already provided for an abrupt cliange 

 to the ordinary form of leaves. Some seedlings show more gradual 

 transitions from the cotyledons to the ordinary leaves, and some 

 have specialized reduced leaves between the cotyledons and the 

 ordinary foliage leaves, as in Persea gratissirmi and Citrus tiifoliata. 

 The cacao tree often produces similarly reduced scalelike leaves on 

 many internodes near the ends of the upright shoots in addition to 

 two kinds of functional leaves, the ordinary leaves of the upright 

 shoots being different from those of the lateral or whorled branches. 

 Many plants have small entire leaves like those of seedlings at the 

 base of each new shoot, as in the vegetative branches of cotton. In 

 grasses and palms the basal joint of each branch or inflorescence 

 bears a small bladeless sheath, called the prophyllum, similar to the 

 first leaves of seedlings. Pines, junipers, and eucalypts have a dis- 

 tinct juvenile type of foliage in young plants that entirely disappears 

 in adults, though it is recalled to expression when growth is forced 

 from dormant buds after severe cutting back. 



Many herbaceous plants have the so-called radical leaves at the 

 base of the stalk much larger and of a very different form from those 

 farther up, a condition that doubtless passes by numerous gradations 

 into the more definite types of dimorphism shown in Hibiscus and 

 Gossypium. 



The erect fruiting branches of the English ivy are upright and 

 bushy and have more rounded leaves than the familiar creeping stems. 

 De Vries has shown that the so-called variety arborea represents 

 merely rooted cuttings of the fruiting branches that continue the 

 upright habit of growth. De Vries also found that the seedlings of 

 such a plant were of the usual creeping form, and came to the con- 

 clusion that the upright habit was ''not inherited." He states: ^ 



In 1893 I sowed the berries of an older plant of this kind, in this case an ivy bush 

 of about 2 meters, and obtained over a thousand seedlings. These still grow in our 

 garden and have made, up till now, exclusively creeping stems and branches. The 

 arborea form is evidently not inherited. 



In the same way it might be said that the characters of butterflies 

 are not inlierited, since they do not appear in the caterpillar stage 



1 De Vries, H. The Mutation Tiieory, 1909, vol. 1, p. 44. 

 221 



