so 



THE LEAF 



g6. — Winged petiole of 

 Polymnia.^ 



97- 



- Water cups of Silphium 

 perfoliatuni. 



instance, do housewives sometimes set the feet of their 

 cupboards in vessels of water ? 



60. Protection against Excessive Light and Heat. — With 



plants growing in very hot, dry climates, or in exposed 



situations, it is often necessary to guard against too rapid 



transpiration by shutting off the 



direct rays of the sun from the sto- 



mata, just as we close our blinds in 



summer to keep the heat out. The 



common blackberry lily (^Belarn 



candd) of our old red hillsides, and 



98.— Cross sections of the Others of the iris family, to which 



leaf of sand grass:,,, unrolled -^ belongs, havc their leaves ranged 



in Its ordinary position ; b and ° ° 



c, rolled up to prevent too vertically SO as to cxpose only the 



rapid transpiration. ^jpg ^^ ^j^^ f ^^^ ^j^^g ^^ ^j^^ nOOnday 



sun. Many swamp herbs like the sweet flag {Acorus 

 calamus), the cat-tails, and yellow-eyed grass i^Xyris) have 

 the same habit, the pools and marshes in which they grow 

 often becoming dry in summer ; and moreover, even though 

 there may be plenty of moisture, they are very dependent 

 upon it and need to retain a good store. Strongly revo- 

 lute margins, such as are found in many sand plants 

 growing along the seashore, produce the same effect by 

 inclosing the stomata in the hollow trough or cylinder 

 formed by their recurved edges. 



