28 COMPOUND ORGANS OF PLANTS. 



exemplified in the common garlic, (fig. 6.) In this respect the 

 bulb behaves exactly like a leaf-bud after it has been lengthened 

 into a branch. One or more of these young bulbs or cloves 

 may develope as flowering stems the next season, and thus the 

 same bulb survives and blossoms from year to year. 



In some plants, as in Lilium bulbiferum, (fig. 7,) bulbs are 

 produced on the stem in the axils of the leaves, which, when 

 detached from the stem -and placed on the ground, will grow 

 into independent plants. These bulbs are called bulblets. 



The tuber is a subterranean branch which is arrested in its 

 growth, and becomes remarkably thickened in the place of 

 being elongated. It is seen in the common garden potatoe, 

 the eyes of which are true leaf buds. Hence these tubers 

 when cut into slices, provided the slice contains an eye, will 

 grow and become independent plants. 



In the lower forms of their development stems are so weak 

 that they trail along the ground, never rising from the earth's 

 surface. * In other instances these weak stems have a tendency 

 to grow vertically ; and when this is the case they either twine 

 in a spiral around the more vigorous herbage in their vicinity, 

 or the roots of the phytons take a horizontal development and 

 exhibit themselves all along the side of the axophyte, as in the 

 Ivy and Virginian creeper. By such aerial or adventitious 

 roots such plants attach themselves to the surface of rocks 

 and the bark of trees, and thus elevate themselves to the air 

 and light. 



In somje plants, such as the pea and vine, the leaves are 

 developed as organs of support. By the non-production of the 

 parenchyma, and the development of the fibro-vascular system, 

 an organ called a tendril is produced, which has a tendency to 

 twine round any body with which it may come in contact. 



