370 THE NURSERY-MANUAL 



soon crowd each other, and growth is checked, causing them to 

 ripen prematurely. Good sets should not be more than a half inch 

 in diameter. Very small onions which are selected from the 

 general crop called " rare-ripes" are sometimes used as sets, 

 but they are usually too large to give good results. 



Some onions the " multiplier" or "potato onions" in- 

 crease themselves by division of the bulb. The small bulb, which is 

 planted in the spring, splits up into several distinct parts, each one 

 of which will multiply itself in the same manner when planted the 

 following year. 



Ophiopogon. LiliacecB. 



Propagated by division. See lAliaeece, page 349. 

 Oplismenus. Graminece. 



Propagated by divisions of the rooting stems; seeds, when 

 obtainable. 

 Opuntia (Prickly Pear. Indian Fig). Cactacece. 



Seeds grow readily, sown as soon as ripe in ordinary sandy soil, 

 either in the house or outdoors. The joints or pads root freely if 

 laid on sand. It is customary to allow these cuttings to dry several 

 days before planting them. See also Cacti, page 261. 

 Orach (Atriplex hortensis). Chenopodiaceas. 



Raised from seeds, sown where the plants are to stand. 

 Orange (Citrus Aurantium, C. sinensis and others). Rutaceoe. 

 (H. H. Hume.) 



The orange, in common with other fruits of the genus Citrus, is 

 generally propagated by working on orange seedlings or seedlings 

 of related species. The stocks are grown from seeds of sour orange, 

 sweet orange, rough lemon, grapefruit and Poncirus trifoliata. In 

 the orange districts of the world, sweet orange stocks have almost 

 wholly disappeared from use in nursery practice owing to their 

 susceptibility to various root and trunk diseases. 



Sour orange stocks are most commonly used, and except for special 

 soil or climatic conditions, are to be preferred. Poncirus trifoliata is 

 adapted to colder sections and heavy soils and its use has greatly 

 extended orange culture into the colder regions ; this is the tri- 

 foliolate orange, commonly known as Citrus trifoliata. Rough 

 lemon stock is suited to warmer climates and to soils deficient in 

 plant-food. Grapefruit stock is sometimes employed in special 

 cases for rather low lands. 



