252 



LEAVES 



A . Needle-like Leaves. Pine trees bear the needle-like 

 leaves which are probably most familiar to you. The 

 common varieties of pine may be distinguished by the 



character of their 

 needles. The advan- 

 tages and disadvan- 

 tages of needle-like 

 leaves as compared 

 with broad leaves 

 have been noted in 

 the preceding sec- 

 tion. Since these 

 leaves live and work 

 during the winter, it 

 is not surprising to 

 find in them thick 

 protective layers of 

 tissue surrounding the mesophyll. The stomates are found 

 at the bottom of pit-like depressions. (See Figure 8p.) 

 These structures, combined with the comparatively small 

 surface exposed and with the small water content, enable 

 these leaves to survive through the severest winters. 



B. Leaves as Insect Traps. You may have heard of 

 carnivorous plants. You may even have seen them in 

 conservatories. They are often kept there as curiosities. 

 Carnivorous means meat-eating. Only a few kinds of 

 plants possess this power of using animals as food. The 

 animals used are insects, and the organs which capture 

 them are leaves. Two principal types of plant insect - 

 traps are found : one is the pitcher type, the other the steel- 

 trap type. 



FIG. 89. Cross section of pine needle. Note the 

 layers of protective cells just under the epi- 

 dermis. Note that the stomates are at the 

 bottom of little pits. The vascular tissue is in 

 two strands in the center. The rings of cells in 

 the mesophyll indicate cross sections of resin 

 ducts. 



