INTERNAL STRUCrXTRE OF LEAVBS. 



157 



204. — Another curious leaf structure is to be seen in 

 Stipa spartea, the Porcupine Grass of the interior ; each long 

 harsh leaf is longi- 

 tudinally channel- 

 led on its upper 

 surface, which, by 

 the twisting of the 

 basal portion of 

 the leaf, becomes 

 apparently the low- 

 er, and the chlo- 

 rophyll-bearing pa- 

 renchyma is con- 

 fined to the sides of 

 tlie channels (Pigs. 

 135 and 136). At 

 the bottom of each 

 channel the epider- 

 mal cells are pe- 

 culiarly developed 

 into a liygroscopic 

 tissue, which, by 

 contracting, closes 

 the channels and 

 rolls the leaf to- 

 gether, as always 

 takes place in dry 

 air. 



(fl) Many Monocoty- ^^^ 

 ledons — as, for exam- 

 ple, Iris and Indian 



affn-rA «nn/l ot^o Kg. 134.— TraiiBverBe secdoii of thn leaf of SUpUum 



corn — anora gooa ape- ii^ijiiatum. e, cpidennis of the upper i-urface ; e'. epi- 



cimens of very youiia* dermis of the lower surface; p, palisade tissue of the 



. -D J n upper portion of the leaf; p\ palisude tissue of thu 



leaves, ay caretully jo'^^^r part of the leaf ; «, a Btoma seen in transverse 



removing the outer section, x 835.— From a drawing by the author, 

 leaves in succession all stages of leaf-development may be obtained.^^^ 



south— i.«., with the leaf-planes parallel to the plane of the meridian- 

 see articles in the American Naturalist : 1870, p. 495 ; 1871, p. 1 ; 

 1877, p. 480. 



