344 



EXPERIMENTS WITH PLANTS 



Light. — The effect of light on the plant is ordinarily 

 much the same as that of dryness. In fact, some of 

 the effects of strong light are due to the increased trans- 

 piration which it produces. In the case of the desert- 

 plants, etc., the effects of the two are difficult to 

 distinguish. There are, however, many effects of light 

 which are independent and are manifested equally 



199. Leaves of Prickly Lettuce seen in cross-section: (a) sun leaf, (6) shade leaf. 



well when the plant is grown in a saturated atmos- 

 phere. 



Some plants (sun -plants) prefer the direct sun- 

 shine, while others grow only in the shade (shade- 

 plants). The latter (e. g., many Ferns, etc.) have 

 leaves of paler color, relatively large and thin, and 

 not well adapted to withstand direct sunlight : if 

 exposed to it they soon die. Similar differences may 

 be found in leaves growing on the same plant when, 



