226 APPLIED BIOLOGY 



season, or else the seeds are started one year and form small 

 onions (" sets ") which are planted the next spring. In this 

 case one seed forms one set, and one set forms one onion bulb, 

 which when mature forms flowers and seeds ; hence multiplica- 

 tion can be only by seeds. Some other kinds of onion bulbs 

 behave differently in that the bulb which is planted divides 

 into a group of little bulbs (bulbels). The multiplier or 

 potato onion does this, and garlic is similar. Each of the 

 little bulbels may be planted and will soon grow to full size, 

 and then begin to form more bulbels. Multiplier onions 

 occasionally produce seed, but gardeners commonly use the 

 bulbels for planting. A third kind of onions form " top 

 onions " or bulblets on the flower-stalks, sometimes mixed 

 with some flowers. These small bulblets may be planted 

 next season and soon grow to usable size, but if left in the 

 ground, they will send up flower-stalks which produce bulblets. 

 The so-called " Egyptian onions " and " tree onions " are 

 top-onions. In the wild garlic some of the flowers are fre- 

 quently replaced by bulblets. The above ways of growing 

 different varieties of onions illustrate the methods of propa- 

 gating many bulb-producing plants. Hyacinth, narcissus 

 or daffodil, many lilies, crocus, and tulip are examples of 

 flowering plants which are usually grown from bulbs and 

 rarely from seed. 



Without the aid of man some flowering plants may propa- 

 gate from roots, stems, leaves, bulbs, in addition to seeds. 

 By man's help many of them which do not naturally propa- 

 gate without seeds can grow from parts of the plants like 

 stems and roots. For example, cuttings or slips may be cut 

 from stems of almost any plant and if properly set in moist 

 soil will form roots and develop into a new complete plant. 

 This is the familiar method of starting geraniums, coleus, and 

 other house-plants; and dozens of shrubs (e.g., currant), 

 vines (e.g., grape), and trees (e.g., willow) are commonly 

 started from cuttings of stems. Go into any greenhouse 



