158 



BOTANY. 



In tliis way often much light will be thrown upon the morphology 

 of leaf parts.* 



(b) Among Dicotyledons it is generally best to select those whose 

 _ young leaves are least downy or hairy, 

 * * * * otherwise the difficulties of the examina- 



tion are greatly increased. The lilac is 

 one of tbe liest for this purpose. Longi- 

 tudinal sections, prepared as in the ex- 

 amination of young stems, should be 

 made. 



(c) The young leaves in the winter buds 

 of the hickory are instructive, as showing 



Fig. 136. A part of a trans- 

 verse section of the 1. af of fitipa 

 gpartea in the position it as- 

 sumes i.e., with what is really 

 the upper surface turned toward 

 the earth. /,/, rib*, each con 



chlorophyll-bearing paren 

 (figured dark in the cut), 



(d) The study of the arrangement of 



between these are the masses of 

 ?nchyma 



x leaves is most interesting in the twigs 

 and cones of the Conifers, and the stems and heads of the Composites. 

 The student should, however, before spending much time in the 



Fig 136. Transverse section of one of the ribs of the leaf of fitipa f/>artfa. tp, 



chlorophyll-bearing parenchyma ; , , portions of the epidermic eoattuniug stc.in;ita : 

 t when the leaf rolls up. The blaiik 

 ccupied by chlorophyll-bearin 



X 125. From a drawing by the author. 



, , 



he, he, hygroscopic cells, which contract when the leaf rolls up. The blaiik space on 

 the left shows the extent of the cavity occupied by chlorophyll-bearing parenchyma. 



examination of the more difficult forms, study the twenty-sixth section 

 of Sachs' "Text-Book of Botany," and the whole subject of the 



* In illustration of this, the Iris itself may be cited. Its leaf is 

 usually spoken of as made by ihe folding of its upper surface upon 



