1901.] NATURAL SCIENCES OF PHILADELPHIA. 307 



are extremely variable, the variations beiug within wide limits. 

 The first leaf, au evolved one, was the largest one measured. If 

 it is contrasted with a juvenile leaf No. 15, one of the smallest 

 leaves, a wide divergence is noted. It is important, however, to 

 notice here that an absolute comparison cannot be drawn, because 

 of the wide variation in parts of. the leaves themselves. For ex- 

 ample, although in most of its dimensions leaf No. 15 is a small 

 one, yet its midrib is longer than the midrib of No, 9, which is 

 a middle-sized one. Therefore in comparing the large leaf No. 1 

 with the smallest leaf No. 15, these variables must be taken into 

 consideration. 



It is important to distinguish between the juvenile and adult 

 forms of leaves. The differences in the construction of the juve- 

 nile and adult form are in general more different when the external 

 conditions to which they are severally adapted are different, 

 whilst if these do not operate, the primary leaves with which we 

 have here first to deal are only arrested formations. In many plants 

 reversion of the adult to the juvenile form frequently occurs. 

 Evidently leaf No. 15 represents a juvenile form of leaf, that is, 

 one derived from a rootstock which has been directly formed from 

 the seedling plant, and the larger more deeply lobed leaves, such 

 as No. 1, represent forms derived from a rhizome which has per- 

 sisted for some years. In making these statistical measurements, 

 therefore, the amount of the difference between the juvenile and 

 adult forms is clearly set forth, as also the adult leaf variations 

 mathematically expressed. 



In the accompanying tables (II and Ila), L. = length, W. = 

 width of lobe, a star (*) beside a number indicates that the deter- 

 mination of the width of that lobe was made by measuring the 

 length of a perpendicular from a line drawn from the base of a 

 leaf to the apex of the lobe. The measurements were made from 

 a basal point where the primary veins of the leaf meet. Fresh 

 leaves were used in making the sketches from which the dimensions 

 later were taken. The lowest point of the leaf was ascertained by 

 measuring from the vein of the last and lowest lobe of the leaf on the 

 right and left sides to the apex of the most projecting curve or 

 angle toward the base of the leaf. The breadth of the leaf was 

 determined by measuring across the widest portion of the leaf 

 lamina. 



