198 THE LEAF 



they represent, and that the value of the fraction will represent the 

 divergence of, or part of a circle between, any two leaves adjacent in 

 the cycle or spiral — that is, the number of degrees between such leaves 

 will equal that fractional part of 360 degrees. 



Antidromy. — As to the direction which the spiral takes, it may be 

 either from right to left or from left to right. It is supposed that each 

 kind of plant, at least of the higher classes, produces two forms or 

 "castes," depending in some not yet perfectly determined way upon 

 the relative positions of the respective ovules from which they originate. 

 The tendency of these two castes to manifest their growth or develop- 

 ment in opposite directions has been called Antidromy. Among numer- 

 ous other phenomena attributed to antidromy is this starting of the 

 leaf-spiral in opposite directions in plants of the two castes of any 

 species with this form of phyllotaxy. 



The Scattered Arrangement. — Occasionally, leaves appear to be 

 irregularly disposed upon the stem — that is, they are not whorled, nor 

 does the law of alternate phyllotaxy appear to apply to them. This 

 arrangement is called Scattered, and the explanation is different in 

 different cases. 



Tufted Leaves. — When a stem is so shortened that the leaves are 

 crowded upon it in the form of a regular rosette, as in the house-leek, 

 the arrangement is called Tufted. 



Fascicled Leaves. — When similarly short, but the leaves few and 

 irregularly crowded in a little bunch, the arrangement is Fascicled. 



The two regular forms of leaf arrangement above described can be 

 traced in greater or less perfection through floral bracts and involucres, 

 and into and in many cases partly or wholly through the flower itself. 

 While such arrangement in the flower is in many cases entirely verti- 

 cillate and in most cases partly so, it has been quite clearly shown that 

 many flowers have certain of their parts arranged upon the spiral plan. 



