94 PRACTICAL COURSE IN BOTANY 



from the axils of the scales, thus revealing their leaflike 



nature. 



That bulbs are only modified buds is further shown by 



the bulblets that sometimes appear among the flowers of the 

 onion, and in the leaf axils of certain lilies. 

 They never develop into branches, but drop 

 off and grow into new plants just as the 

 subterranean bulbs do. 



The bulbs of the onion and hyacinth are 

 still further modifications, in which the scales 

 consist of the thickened bases of leafstalks 

 that are dilated until each one completely 



of rron^n'dhS envelops the growing parts within. 



lengthwise, showing io8. Moiphology is the part of botany 



the base enlarged ,i , , , c ir. • • r j 



into the coat of a that treats 01 the origm, lorm, and uses 

 *'""'• of the different organs of plants, and of 



the modifications they undergo in adapting themselves to 

 changes of condition or function. Organs or parts that 

 have the same origin but have become adapted to dif- 

 ferent functions, like the flattened stems of the butcher's- 

 broom or the bulb scales of the lily, are said to be 

 homologous; those that are different in origin but adapted 

 to the same function, as the sweet and common pota- 

 toes, are analogous. In other words, homologous organs 

 are morphologically alike, but may be physiologically dif- 

 ferent ; analogous organs are alike physiologically, but 

 differ morphologically. 



109. Economic value of stems. — We probably get a 

 greater variety of economic products from the stem than 

 from any other part of the plant. Consider the vast 

 amount of food stored in underground stems like the potato ; 

 the resins, gums, and sugar found in the sap of plants 

 like the sugar cane, the pine, and India-rubber trees; the 

 medicines, dyes, and extracts obtained from the tissues ; the 

 valuable fibers, such as flax, jute, and hemp, furnished by 

 the bast; the wood pulp for making paper; and the timber 



