256 VEGETABLE ORGANOGRAPHY. 



termSj believed in another sense, does not answer 

 exactly to that which I propose. 



In order to give a true idea of the lobes of leaves, it 

 is sufficient to set out with the same idea of the foli- 

 aceous structure : a long or short petiole is formed of 

 a bundle of fibres ; these, diverging after two different 

 systems, separate from one another and form the nerves, 

 each of which ramifies after a given system ; and thus it 

 proceeds until all the fibres of the bundle and all the 

 vessels of the fibres are isolated. Each fibre being formed 

 of vessels and cellular tissue intermixed, the latter is 

 developed when the separation of the vessels leaves 

 room for it, and then it tends to fill up the intervals ; 

 these being in this manner filled with cellular tissue, 

 the whole appears entire : but it may happen that the 

 vessels diverge too much in proportion to the increase 

 of the cellular tissue, so that it cannot occupy all the 

 interval which separates them, and then it fills up only a 

 part of the angle which they form between them ; and 

 from the cellular tissue not filling up the entire interval, 

 it results that there is a retreating angle, which is called 

 a Sinus. 



When this phenomenon takes place in the last ramifi- 

 cations only of the nerves, small projecting angles are 

 formed, which are called Teeth, or indentations, and 

 little sinuses, which have not received any particular 

 name. If the teeth are sharp, the margin is said to be 

 SERRATED. If they are very obtuse, it is crenated. 



All that I have said of the vessels or fibrils of a fibre 

 may take place from analogous causes between the 

 lateral nerves of a pinnated leaf. Let us suppose that 

 these nerves are very near each other ; the parenchyma 

 formed by their ramifications may be developed so as to 

 reach that which proceeds from a neighbouring nerve, 

 and in this case it unites with it before the period 



