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 
We that are dilated until each one completely 
of ne on aii, envelops the growing parts within. 
lengthwise, showing 108. Morphology is the part of botany 
‘oA Ageia aaa that treats of the origin, form, and uses 
bulb. 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 
