AN ENCYCLOPEDIA OF HORTICULTURE. 



495 



Onion continued. 



Yellow Danvers. Bulbs of medium size, with small base and 

 tine slender neck ; flesh very firm throughout, of fine quality. A 

 fine and distinct variety, which ripens off freely and keeps well. 

 See Fig. 741. 



The following are varieties of Onion that are distinct 



in habit from those already enumerated. They are useful 



to grow in small quantities, as sometimes they come in 



when others are not procurable. 



Egyptian, Tree, or Bulb-bearing Onion (GARDEN ROCAM- 

 BOLE). This throws up a stem from the bulb, which has to be 

 planted, and produces a number of small bulbules, about the size 

 of marbles, on the top, that are excellent for pickling. Offset 

 bulbs are also formed underground ; and from these, and the other 

 small ones produced on the stem, the variety is propagated. 



Perennial Tree or Top Onion. This is somewhat similar to 

 the EGYPTIAN, but the bulbules are smaller, and none are pro- 

 duced underground. The plant is perennial, and has long, fibrous 

 roots. 



Potato or Underground Onion. A variety cultivated some- 

 thing like Shallots. Small bulbs are planted singly, and around 

 them new ones are formed. They are of irregular shape, of fair 

 quality, and useful for an early supply. This variety is not pro- 

 pagated from seeds. 



Welsh Onion. This is a herbaceous perennial, with long, fibrous 

 roots ; it forms no bulbs. There are two varieties, the Red and 

 the Green, cultivated for the use of their tops, or leaves. Propa- 

 gated by seeds, or by division of the roots. 



ONION FLY (Anthomyia Phorbia ceparum). This 

 insect is at times most hurtful to Onions, the larvae 

 burrowing into, and eating, the bulb scales, near the 

 base, in companies of from two or three to one hundred, 

 or even more. These attacks are very serious in some 

 localities, the greater part of the crop being often 

 severely injured. The bases of the thick leaf-scales rot, 

 and the plants are easily pulled up, leaving the decaying 

 bulb and the maggots in the soil. 



The flies are not unlike common house-flies in general 

 appearance. They are of a blackish colour, thickly 

 powdered with grey ; the sides of the thorax are pale, and 

 there are three dark lines on the back. In certain lights, 

 the abdomen has a whitish lustre on it, with, in the male, 

 a darker median stripe. The eyes are separated, in the 



Fro. 742. ONION FLY, LARVA, AND PUPA. 



1, Lines showing Natural Spread of Wings and Length of Body of 

 the Fly ; 2, Line showing Natural Length of Larva. 



male, by a slender, black, white-bordered line ; the face 

 has a pale lustre, and the forehead is black, as are the 

 antennae and palpi; the legs are pitch black, the wings 

 being pale grey, and the poisers white. The length of 

 the insect is about in. In the female, the forehead is 

 broad, with a reddish-brown, vertical median stripe, and 

 the body is more ochreous in colour than in the male. 



Life History. The flies emerge, in early summer, from 

 the brown pupae, which have remained all winter under- 

 ground, sometimes in the Onion, but usually near it in 

 the soil. The female generally lays her eggs, five or six 

 on each plant, on the leaves, just above the soil; and 

 from these emerge larvae, which bore downwards in the 

 soil, and into the leaf bases, causing the whole Onion 

 ultimately to rot under their attacks. They are nearly 



Onion Ply continued. 



white, with yellow stigmas, smooth and shining, tapering 

 (but headless) in front, and blunt behind. When full- 

 fed, they burrow into the soil, and there become changed 

 into chestnut-brown wrinkled pupae. The fly, larva, and 

 pupa, are shown in Fig. 742, and a diseased bulb in 



Fio. 743. SECTION OF ONION ATTACKED BY LARVAE OF ONION FLY. 



a, a, Groups of Eggs and Young Larvse ; 6, Hole made by Larva in 

 Entering the Bulb ; c, Direction of Course followed by Newly- 

 hatched Larva to reach Base of Bulb ; d, Burrow of Larva, in 

 Bulb, with Larva lying in it. 



Fig. 743. The entire development occupies from four 

 to six weeks, so that several broods may appear in a 

 summer. The first sign of attack by the larvae is that 

 the outer leaves become yellow, and fall, withered. The 

 habitat in the bulbs protects the larvae from injury, and 

 from direct means of destroying them, unless the Onions 

 are destroyed. 



Remedies. Prevention is better than cure ; and, for 

 the safety of future crops, it is well to dig up and 

 remove any plants that show signs of turning yellow, 

 especially where the flies have been observed. The 

 diseased bulbs should be dug out carefully ; and they, 

 and any larvae that creep out, should be destroyed. If 

 this is done sufficiently early, all the larvae should be 

 got rid of ; but if deferred, they will have left the 

 bulbs, and have turned into pupae in the soil, in which 

 situation they are less easily reached. Deep trenching 

 of the soil in autumn is of use to destroy the pupae, 

 and farmyard manure, dug in during- the operation, 

 strengthens the plants. Applications of soot or gypsum, 

 and of gas-lime, to the soil have been found useful; 

 as have also soapsuds, and water from pigstyes, and, 

 best of all, the use of paraffin oil, in the proportion of 

 about loz. or 2oz. to a gallon of water. Sulphuric acid 

 has been recommended, but is hardly suitable, as it 

 is dangerous to the plants. Scattering the plants in 

 small groups among other crops hinders the passage of 

 larvae from plant to plant. 



ONISCIDJE. A family of Crustacea, popularly known 

 as Woodlice, or Slaters. The Crustacea include a large 

 number of animals, which, like insects, have the body 

 jointed, or forming rings of hard substance, to protect 



