106 THE PI.ANT WORIvD 



Juvenile and Adult Forms of Bloodroot. 



By John W. Harshberger. 



A PLANT in its development from youth to old age passes through a 

 series of marked changes, chemically and structurally considered. The 

 first stages may be called the juvenile stages, and when the climax of de- 

 velopment is reached the adult stage begins. The difference between 

 the juvenile stages and the adult form may be more or less great. These 

 two stages naturally include series of developmental processes which pass 

 one into the other without distinct limitation. Thus, for example, the 

 primary leaves of the broad bean, Vicia/aba, differ greatly in configura- 

 tion from the succeeding ones ; they are reduced to small three-toothed 

 leaflets, the middle tooth representing the leaf -blade, the lateral ones the 

 stipules. The primordium of the leaf has remained stationary here at a 

 very early stage, and in subsequent leaves experiences only an increase 

 in size and no further morphologic differentiation takes place. We can 

 prove this experimentally. The axillary shoots which spring from the 

 base of the plant all possess the same form of leaf. If the chief shoot be 

 removed above the primordium of a lateral shoot, this will be forced to 

 grow out at an early period, and instead of the primary leaves there will 

 be found upon it, according to the degree of development to which it had 

 attained, the most varied intermediate forms between the primary leaves 

 and the foliage leaves, or the typical foliage leaves.* 



A somewhat similar case is found in the bloodroot (^Sa?ig7nnaria cana- 

 densis Iv.). This plant is met with commonly in our eastern woods and 

 forests and displays, as the botanists of our country have no doubt fre- 

 quently noted, great differences in the form and lobing of its leaves. 

 These forms may be reconciled with each other and arranged in a series 

 if the above-mentioned facts with reference to the juvenile and adult 

 stages are taken into consideration in making a comparison of the vari- 

 ous kinds of leaves of the bloodroot. After the seed has germinated and 

 the two cotyledons have unfolded and while one of them still remains 

 attached to the seed coats, the hypocotyl of the embryo plant begins to 

 swell to form a fusiform enlargement. Coincident with this, the first 

 leaf makes its appearance. This juvenile leaf is somewhat reniform with 

 an undulate margin and in most cases (figs. A and C) with a rounded 

 tooth at the apex. Stages of about the same age are represented in 

 figures A, B, and C. As the fusiform hypocotyl enlarges and as new 

 secondary roots appear growing out from it, the first leaves are replaced 

 by other juvenile forms much larger in size and usually with three dis- 



•GOKBKi,, Organography of Plants, E;ng. transl., Part I, General Organography, p. 156. 



