10+ POPULAR SCIENCE MONTHLY. 



nous substances from the leaves and the stem to the grain and the 

 later production of starch takes place only when the plant con- 

 serves a considerable quantity of water. If the radiations of a 

 burning sun strike upon a field of wheat the roots of which find 

 nothing to drink in a dry soil, the plant dries up, everything stops, 

 and the last phase of the life of the wheat is abruptly terminated ; 

 the grains remain empty, and the crop fails. 



Persistent rain is no less to be feared. The wheat continues 

 to grow indefinitely, and the migration of the principles is not 

 brought about. I witnessed a very curious example of this in 

 England twenty years ago. I was visiting a farm near London, 

 where cultivation was assisted by irrigation with sewer water. 

 The farm was slightly undulating, and the sewer water was car- 

 ried over the depressions in troughs sustained a few yards above 

 by wooden supports. One of these troughs, being in bad condi- 

 tion, let the liquid fall constantly in a fine rain upon several 

 square yards of a field of wheat. It was July, and, while all 

 the rest of the field was yellow and ready for the harvest, the 

 stools thus watered were still green and continuing to grow, 

 exceeding all their neighbors in height, and giving no signs of 

 maturity. 



A mild temperature and a slightly clouded sky are the favor- 

 able conditions for a good ripening. When the land has been well 

 dug, the seeding regular, and the manure judiciously distributed, 

 all the individual plants in the field will have expanded together, 

 all will have passed simultaneously through all the phases of their 

 development, and in the warm hours of the day, when all is mo- 

 tionless, the surface of the field, the English say, will appear as 

 horizontal as a table. 



There are no great inconveniences in harvesting a little early. 

 The ripening, if not yet complete, will proceed very well when 

 the sheaves are stood up against one another into those " shocks " 

 which are much in use where severe rains are common. On the 

 other hand, there is much advantage in not leaving the wheat 

 standing after it has ripened. Every plant that has matured its 

 seed tends to shed it, and sometimes the seed has powerful organs 

 of dissemination. This is not the case with wheat ; but, although 

 it does not fly off to a distance, it escapes from overripe heads, 

 falls, and is lost. Further, all the organs of plants respire by the 

 aid of the oxygen of the air consuming some of their principles. 

 In the seed the combustion chiefly affects the starch, and a crop 

 which remains standing long diminishes in weight both by the 

 loss of the seeds that fall and by the slow combustion which con- 

 tinues as long as desiccation is not produce^. As soon as a field 

 of wheat is ripe it should, therefore, be harvested, and here is 

 where the reapers, that have been brought to such great perfec- 



