SWEET-CLOVER SEED. 23 



normal in July. Both the precipitation and temperature were about 

 normal at Ames in August, hut most of the precipitation fell before 

 the experiments were commenced. 



In north-central Illinois the seed production of sweet clover was 

 very irregular. Some fields produced an abundance of seed, while a 

 large percentage of the pods on the plants in other fields near by, 

 where the thickness of the stand, size of the plants, and conditions 

 in general were approximately the same, aborted. It was evident 

 that all stands producing a good seed crop were growing on well- 

 drained soil and that those which were not yielding satisfactorily 

 were on poorly drained land. It is well known that sweet clover 

 will produce deep taproots only when the plants are growing in 

 well-drained soil and that a much-branched surface root system will 

 be formed on poorly drained land, and especially when there is an 

 excess of moisture or a high water table during the first season's 

 growth. During this droughty period in 1916 the upper layer of soil 

 became so depleted of moisture that the plants with surface root 

 systems were unable to obtain sufficient water to mature their seed. 

 On the other hand, the lack of precipitation and the high tempera- 

 tures did not affect the moisture content of the subsoil sufficiently 

 to interfere with the normal seed production of deep-rooted plants. 

 According to Lutts (22, p. 47) this same condition was found to be 

 true in Ohio in 1916. 



As a rule, under droughty conditions the second crop of sweet 

 clover will produce a higher yield of seed than the first crop, as the 

 second growth of the plants is seldom more than half as much as the 

 first, thereby requiring less moisture. However, if showery hot 

 weather prevails when the first crop is cut, the end of each stub is 

 very apt to become infected, usually with a species of Fusarium, 

 which kills all the cortex as far back as the upper bud or young shoot 

 and that part of it on the opposite side of this bud to the bud below. 

 If the second bud from the top of a stub is not directly opposite the 

 upper one the decay may extend nearly to the ground. (PL IV.) 

 The destruction of half to two-thirds of the cortex from 2 to 4 inches 

 below the upper bud materially reduces the quantity of water that 

 can be conveyed to the branch above the base of the dead area. 

 Plants thus infected obtain sufficient moisture for seed production 

 only under the most favorable conditions. When the first crop is 

 cut during warm dry weather, and especially when the first crop has 

 not been permitted to make more than a 30 to 32 inch growth, the 

 stubble seldom decays, and in no instance have the plants been 

 observed to decay as far back as the upper buds. 



An experiment was conducted at Ames in the latter part of August 

 and first part of September, 1916, to determine the effect of watering 

 plants that were aborting a large percentage of their flowers and 



