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 

 (Hex\ 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 piuxoby} 



must remember do FlG - 31 - LADY'S SMOCK (Cardamines pratensis). 



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 



Sometimes called Cuckoo-flower. A familiir sprin? flower in moist meadows. The 

 pinnate leaves often bear buds in t'.ieir axils which develop into new plants. 



