726 A TEXT-BOOK OF BOTANY. 



to the Middle United States and sometimes cultivated. The 

 tubers, which resemble artichokes, are more or less elongated or 

 pear-shaped, reddish-brown, somewhat annulate, and internally 

 white or reddish. They have been used as a substitute for pota- 

 toes and contain about i6 per cent, of the following carbohydrates : 

 Inulin, pseudo-inulin, inulenin, saccharose, helianthenin, and syn- 

 antherin. In early spring with the development of the tubers there 

 is formed a small quantity of dextrose and levulose. 



The Globe artichoke of the gardens {Cynara Scolymus) is a 

 hardy perennial and is valued on account of the fleshy involucral 

 scales and torus, which are edible. 



The POLLEN of a number of plants of the Compositae, as rag- 

 weed (Ambrosia), golden-rod (Solidago), aster and chrysanthe- 

 mum, is said to be responsible for the autumnal cold, known as 

 HAY FEVER. A similar disease is produced in spring and early 

 summer by the pollen of certain grasses. It has been found that 

 the pollen grains of these plants contain a highly toxic substance, 

 belonging to the toxalbumins, which is the cause of the disease. 

 By inoculation of rabbits, goats and horses with this toxalbumin 

 a serum containing an antitoxin is obtained which neutralizes the 

 pollen toxin and protects those who are susceptible to hay fever 

 from its attacks. In practice the serum is prepared by injecting 

 the toxalbumin subcutaneously into horses, the serum being known 

 in commerce as pollantin (Fig. 398). 



The pollen of the following plants is toxic : aster, barley, 

 chrysanthemum, convallaria, corn-flower, golden-rod, grasses, 

 honeysuckle, oats, Oenothera, ragweed, rice, rye, spinach, wheat, 

 and zea. The constituents of rye pollen are 86.4 per cent, of 

 organic matter, 10.2 of water, and 3.4 of ash. The organic matter 

 consists of 40 per cent, of toxic substances, 3 of fixed oil, 25 of 

 carbohydrates, and 18 of a non-albuminous substance. The num- 

 ber of pollen grains per gram varies in different plants : from 

 Indian corn being 7,000,000, of rye 20,000,000, of golden-rod 

 80,000,000, and of ragweed 90,000,000. 



The flowers of the Japanese chrysanthemum " Riuno-kiku " 

 (Chrysanthemum sinense japoniciim) yield 0.8 per cent, of a 

 volatile oil containing an optically inactive crystalline iso-camphor. 



