64 



A TEXTBOOK 01'"' BOTANY 



[Ch. hi. 8 



places, in conjunction with tlic daily swing of the sun through 

 the skj^ must insure among them a sufficiency of that bright 

 diffused Ught which, as earlier noted (page 54), is fully as 



effective in food 

 formation as direct 

 sunlight. Further- 

 more, the crowded 

 condition of such 

 leaves tends greatly 

 to restrict tran- 

 spiration, without 

 ecjuivalent check to 

 the access of carbon 

 dioxide ; and such 

 an arrangement has 

 obvious advantage 

 to plants of limited 

 water supply. 



Ovate leaves are 

 typified by those 

 of Lilac (Fig. 36). 

 The petiole, at the 

 larger end, merges 

 into a strong midrib 

 from which spring 

 side veins, which in 

 turn give rise to a 

 network of veinlets. 

 This general shape 

 is the commonest in nature, and associated \\\i\\ the com- 

 monest condition of leaf existence, viz., that in which the 

 blades, neither spread out in one plane nor densely crowded 

 in full sun, are carried aloft and spaced apart on ascend- 

 ing stems and branches, as occurs in our larger herbs, and 

 especially in shrubs and trees. This mode of life is essen- 

 tially intermediate between that associated with orbicular 



Fig. 34. — Ijinear and olher i)arallel-veincd 

 leaves; X -j. Hyacinth, Banana (small), Thri- 

 nax (a Fan Palm), Eucftari'^, a Grass. 



