THE LEAVES OF VASCULAR PLANTS. 261 



diverging, and almost perpendicular upon the inner side, 

 it is Hastate. 



Leaves with curved and simple nerves cannot be 

 emarginated at the base ; they are so but seldom, and 

 then very slightly. When this form is presented, it 

 is owing to the peculiar curve of the nerves which form 

 the limb, as is seen in some species oi Hemerocallis and 

 Musa. 



The emarginations of the apex of leaves, leaflets, or 

 lobes with pinnate nerves, result from two causes : — 1st, 

 From the lateral nerves of the apex being directed for- 

 wards, and prolonged a little more than the middle one : 

 this takes place in most leaves emai'ginated at the apex, 

 2d, From the lobes or leaflets which arise from the 

 extremity of the two sides of a middle nerve being incom- 

 pletely united, and leaving between them a sharp and 

 often very distinct sinus ; it is thus that the pretended 

 simple leaves of Bauhinia are emarginated, because the 

 junction of the leaflets does not take place as far as the 

 apex. (PI. 11, flg. 1.) 



Lastly, in some palminerved leaves, emarginated limbs 

 are found ; this takes place when the middle nerve is 

 very short and the two lateral ones very long, as is 

 seen, for example, in several species of Passijlora. (PI. 

 11, fig. 2.) 



One of the most curious phenomena which the organi- 

 zation of leaves presents, is the presence of holes or 

 gaps, which are naturally formed in the limb of Dracon- 

 tiuvi pertusum. These holes, although sufficiently fre- 

 quent to have given the plant its specific name, are not 

 liowever regular : when the plant is nourished very 

 abundantly, it has few or none, and they are seen to 

 increase in number in those grown in a poor soil ; these 

 holes are of an oblong form, and placed between the 

 principal nerves. All those who understand the manner 



