Sept. 1896.] ROTTENNESS OF TURNIPS AND SWEDES. 127 



sown upon a cut surface, where the germ-tubes could directly 

 penetrate the plant ; further, all attempts to infect the roots by 

 sowing conidia upon the uninjured surface failed. It would 

 therefore appear as if the germ-tubes had not the power to 

 pierce the outer rind, and it is plainly shown that the surfaces 

 exposed by cutting off the tops and tails are the vulnerable 

 points of attack. The swedes are pulled in the autumn or early 

 winter, and the tops and tails cut off, and this is the very time 

 when countless conidia are floating in the air. I have seen, for 

 example, a field with the swedes lying in rows ready for carting, 

 or even the pits being made in a field, side by side with another 

 field in which potato-haulms were decaying and giving off 

 Botrytis-conidia,. There is thus every opportunity for some of 

 these conidia to be sown upon the cut surfaces of the roots, and 

 it is small wonder that so many are infected even before they 

 find their way into the pits, especially when the atmospheric 

 conditions at the end of the year are just those favourable to 

 the germination of the conidia. The damp atmosphere, too, in 

 the pits is particularly suitable for the growth of this fungus. 

 Having destroyed one root, it spreads to the neighbouring ones, 

 extending over the surface until it finds a wound through which 

 it can enter ; at the same time the countless conidia set free will 

 be carried from one root to another, gaining in infective power 

 in each successive generation. 



Action of Frost. 



Many vegetable tissues, especially when containing a large 

 amount of water, are destroyed by the frost. Turnips and 

 swedes form no exception. If pieces of swede are placed in test- 

 tubes and frozen artificially the cells are killed and lose their 

 turgidity, the whole becoming reduced to a soft and rotten mass. 

 To test the action of severe freezing upon the roots and the 

 Botrytis-conidia,, 12 sterilized test-tubes (a — I) were taken, and 

 pieces of swede introduced into 11 of them ; upon three of these 

 {a, b, c) conidia were sown, and in the twelfth (I) was placed a 

 little water containing conidia. These test-tubes were then all 

 frozen by immersion in a mixture of ice and salt, a temperature 

 as low as — 10° C. being maintained for five hours, falling to 

 — 15° C. for the intermediate three hours. The temperature of 

 the test-tubes was then allowed to rise slowly. After under- 

 going this process of freezing three more of the tubes (d, e,f) 

 were sown with the conidia which had been frozen in the tube 

 I, a little of the water containing the conidia being taken out 

 with a freshly drawn pipette and dropped upon the blocks of 

 swede, the plug being only removed for the purpose for an 

 instant. Three others (g, h, i) were sown with conidia which 

 had not been frozen, and the remaining two (j, k) were not 

 opened but kept as control tubes. The 11 tubes were then kept 

 ,at a temperature of 22° C, 



