HI X IUPTIVE BOTANY. 



PART I. 



(fig. 32.} which are partially filled with air, and serve to 

 float the plant, in order that 

 it may be enabled to flower 

 above the surface of the water. 



(43.) Lfntirr//{t: On the 

 stem and branches of trees, 

 and very conspicuously in those 

 of the alder, birch, and willow, 

 there occur certain roughish 

 prominent traces, of a lenticular shape (fig. 33.), which 

 look as if they were fissures in the bark, having their 

 edges turned outwards. These 

 are termed " lenticells ;" and 

 it is at these places that roots 

 are protruded whenever the 

 stem is placed under circum- 

 stances calculated to give rise 

 to them. 



(44.) Stems. As the cau- 

 dex, or main trunk of the 

 root, is not much extended 

 downwards in many plants, so 

 there are many stems which 

 are never much developed up- 

 wards; but the flower-stalk 

 and leaves appear to rise immediately from the crown of 

 the root. Plants possessing this character are called 

 "stemless." Strictly speaking, however, there are no 

 phanerogamous plants which are entirely without this 

 fundamental organ, although it is often reduced to a 

 mere flattened disc. Occasionally it assumes a bulb- 

 like form, as in the Cyclamens (fig. 34.), where 

 the large woody mass from whence the flowers and 

 leaves arise, is a true stem. In some plants, the stem 

 is wholly beneath the surface of the ground, forming 

 the " subterraneous stem," or " rhizoma ; " but most 

 frequently it rises above it, and composes " the aerial 

 stem," which is called a " trunk," " culm," c. ac- 

 cording to its structure. 



