28 THE DEVELOPMENT OF RAW COTTON 



This cause of germination failure is common in some 

 countries , though not in Egypt ; but even there it may be 

 found. Seed sown in very lumpy soil will not be tho- 

 roughly wetted for a sufficient time, and seed sown too 

 early in the spring may fail from the same cause. The 

 latter is a rather curious point. It would at first sight 

 appear that cold was the limiting factor, but neighbouring 

 seeds will come up freely, and the failures themselves will 

 germinate on a second watering. The cause of failure is 

 simply that at the lower temperatures the absorption of 

 water by the seed-coat is too slow, from purely physical 

 causes, unless the seed is thoroughly and continuously 

 in contact with soil- water. 



The reader may have noticed that, in speaking of the 

 cooling effect of evaporation upon the temperature of 

 the stem tissues, we phrased the necessary 



^ i condition as "ample water around the roots," 

 the Plant. 



and not merely as ample soil- water. The 

 reason for this is that the root may dry the soil- 

 particles which lie near it. The author first showed in 

 Egypt that the cotton-plant stood in a rather extreme 

 attitude towards its water-supply, which might almost 

 be described as one of greed and improvidence. These 

 results have since been confirmed by Professor Lloyd for 

 the United States with the Upland crop, so that there is 

 some justification for believing that they are general. ^The 

 phenomena are most marked in the later stages of the 

 plant's growth, and do not begin to exert much limiting 

 control until after flowering has begun, provided that the 

 seedlings receive a reasonable water-supply. The reason 

 for this is simply the increasing area of leaf-surface, 



