332 On the Failure of the Red Clover. 



the sap of the plant becoming frozen, and the air which is con- 

 tained in it expelled among the sap-vessels ; the heat of the sun 

 then expanding, the confined air, before re-absorption of it by the 

 frozen sap can take place, bursts the vessels of the plant. This is 

 proved by the fact that any frosted plant may be preserved if it 

 be gradually thawed by either pouring cold water upon it, or by 

 protecting it from the sun's rays. Several hundred plants of red 

 clover from different localities were examined during the winter, 

 and the same effects were always visible. 



A number of plants were taken up and placed in a stove in 

 their native soil, having a temperature of 60° to 65°. Of those 

 taken up in November about one-half continued to live, while of 

 those taken up in January all died ; some of the latter had their 

 soil changed, but they also died away in about ten days. Some 

 of those plants which were taken up early in the season, sur- 

 vived, because their sap-vessels were not irremediably damaged, 

 while in those taken up later, the vessels were destroyed to an 

 extent incompatible with the life of the plant. 



It being proved that the clover crops are destroyed in this 

 country by the frost, the next inquiry is, why are they injured on 

 particular soils, or sometimes on a soil where this crop has been 

 successively grown, as every third, or every fourth year ? Upon 

 certain soils of the new red sandstone at Fishlake and Fenwick, red 

 clover has been grown every third year for a series of years, (this is 

 shown in the "^ Yorkshire Agricultural Report,' p. 125,) while upon 

 portions of the chalk wolds of Yorkshire neither red clover nor 

 w^hite clover can now be scarcely cultivated at all, and it may be 

 safely asserted that it is only upon the more pulverulent soils of 

 the magnesian limestone, of the chalk, and of the sandstones of the 

 coal-measures, and some of the lighter soils of the new red sand- 

 stone and oolite, that this crop is injured by the frost, or that 

 become '' clover sick." If it is destroyed on a stiff soil, it is from 

 an excess of water, and because it is too wet ; the natural home 

 of red clover being a dry compact loam, firm and close on the 

 surface. 



The true answer to this inquiry is, that the remote cause of in- 

 jury by the frost, is owing to the want of a certain degree of cohe- 

 siveness of the particles of the soil among themselves, and hence the 

 soil's power of retaining heat is diminished ; and those plants, par- 

 ticularly clovers, which are impatient of sudden change of tempe- 

 rature, are readily destroyed by the frost.* And soils, by the 



* " The power of retaining heat is nearly in proportion to the weight of a 

 determinate volume of soil, i.e. to absolute weight ; the greater mass an 

 earth possesses in the same volume, the greater will be in general its power 

 of retaining heat. We may, therefore, from the absolute weight of an earth, 

 conclude, with a tolerable degree of probability, as to its greater or less 



