LEAF-BEGINNINGS AND LEAF-FORMS 



253 



ment as the Cherry. In monocotyledons particularly the Grasses the 

 arrangement is often two-ranked (distichous) ; that is to say, the third leaf is 

 over the first, the fifth over the third, etc. ; while on the opposite side of the 

 stem the fourth leaf is over the second, the sixth over the fourth, and so on. 

 A three-ranked 

 (tristichous) arrange- 

 ment is, however, 

 by far the most 

 common among mo- 

 nocotyledons. The 

 cycles in such in- 

 stances are three- 

 leaved, numbers 4, 

 7, 10, 13, etc., each 

 commencing a new 

 cycle. An eight- 

 ranked (octastichous) 

 arrangement (eight 

 leaves in a cycle) is 

 found in the Holly 

 (Ilex), Aconite, and 

 many other plants. 

 The above are, per- 

 haps, the most com- 

 mon varieties of 

 phyllotaxis, but the 

 list is very far from 

 exhausted when 

 these have been 

 enumerated. A Fir- 

 cone is simply a col- 

 lection of modified 

 leaves, arranged in 

 a highly character- 

 istic spiral manner. 



All plants, we 

 must remember, do 

 not possess leaves. 

 The Broomrapes and 

 Dodders, for example those thriftless parasites which feed upon the 

 juices elaborated by the host plants to which they attach themselves have 

 no need of leaves. The Cacti and many tropical Euphorbias are also deficient 

 in these organs, though their spines are really metamorphosed leaves or 

 branches, affording them (as we saw on a former occasion) protection from 



Photo by] [E. Step. 



FIG. 310. LADY'S SMOCK (Cardamines pratensis). 

 ailed Cuckoo-flower. A familiar sprii 



Dmetimes < 



pinnate leaves often bear buds in their axils 



.? flower in moist meadows. The 

 fhich develop into new plants. 



