ACTION OF DRY AND MOIST HEAT ON SEEDS AND SPORES. 31 



added (Montillot). Tetranychus telarius, L. (red spider), which forms 

 on different plants a disease called " la Grise," is very sensitive to 

 moisture and does not stand repeated cold-water spraying long 

 (Thomas). Bryobia ribis (gooseberry acarus) may be fought against 

 by frequent sprinkling of the leaves. Spraying with water can thus 

 be used as a preventive against different species of Fumagine or smut 

 (Capnodiinn), as a means of killing acari, of which the Tetranychus 

 (red spider) is the most widespread and injurious. 



(b) Hot Water acts very energetically on insects and fungi, which 

 die in contact with boiling water. Plants and their seeds generally 

 stand heat better. That enables their parasites to be destroyed with- 

 out injuring themselves. 



Resistance of Insects to Heat. — All insects in seed are destroyed 

 below 100° C. (212° F.). Bruchideae (small weevils, pea-weevils) die 

 in five minutes at 60° C. (140° F.). Ordinary weevils do not stand 

 50° C. (122° F.). Grubs touched by water of 50°-80° C. (122°-176° F.) 

 die without exception. Coleoptera (beetles) which sometimes stand 

 great heat never bear 100° C. (212° F.) (Schribaux, Bussard, and 

 Etienne). 



Resistance of Seed to Heat. — Seeds can undergo a dry heat 

 without injury, whilst the action of moist heat, and of water above 60° 

 C. (140° F.) is often injurious. Seed-corn, with the exception of maize, 

 can support a heat of 100° C. for an hour without its germination 

 being affected. In spite of the considerable loss in water which the 

 grain undergoes in such conditions, seed- wheat, for example, which 

 contained 13 per cent of water before being heated lost 9*4 of water 

 during the operation. Their vitality is not diminished. Of Japhet seed- 

 wheat heated for an hour in a stove at 105° C. (221° F.) 97 per cent 

 still germinated; at 115° C. (239° F.) 95 per cent; at 116° C. (240-8° 

 F.) 93 per cent ; at 120° C. (248° F.) 56 per cent ; at 125° C. (257° F.) 

 4 per cent. [Potatoes dipped in boiling water do not germinate.] 



During researches on the Alucite Doyere likewise succeeded in 

 heating seed-wheat dried in vacuo to 100° C. (212° F.) without it 

 losing its faculty of germinating. By previously drying seeds at a low 

 temperature Jodin heated grains of seed-wheat to high temperatures 

 without alteration. Peas and garden-cress seed heated directly to 98° 

 C. (96-4 F.) for ten hours were no longer capable of germination, whilst 

 others submitted to the same heat for the same time stood the heat 

 perfectly, after being heated for twenty-four hours to 60° C. (140° F.). 

 The peas retained a germinating capacity of 60 per cent. Therefore, if 

 seed be heated in such a way as to allow the water to evaporate pre- 

 viously, by heating in an open vessel or in presence of such substances 

 as sulphuric acid, calcium chloride, and quicklime, they undergo no 

 alteration. Seed-peas under such conditions stood heating for 206 

 days at 40° C. (104° F.). 



Resistance of Fungi to Heat. — Fungi spores are generally re- 

 markably sensitive to moist heat, but per contra they stand dry heat 

 well. Schindler found that the spores of the Ustilaginecs which re- 

 sist very great dry heats, are rapidly injured if the hot medium is 

 saturated with water vapour. In these conditions the spores of black 



