438 



BOTANY OF CROP PLANTS 



mon in red ckn-er, the larger percentage usually being in 

 the first crop. I'liis is probably one of the chief reasons why 

 the second cro[) of clover is more commonly used for seed. 

 An additional advantage in harvesting the second crop for 

 seed rather than the first is that the farmer is able to get two 

 crops in a season, for if the first crop is allowed to seed, there 

 is insufficient food supply, and in some instances a season too 

 short, for the development of a vigorous second growth. In 

 addition to the reason given abo\e for the 

 relatively hght yield of seed in the first croj), 

 it is claimed that pollinating insects are not 

 abundant enough, and that the plant is occu- 

 pied with the production of new shoots rather 

 than reproductive activity. In general, a 

 rank-growing plant is not a good seed producer. 

 When the capsule is mature, the stylar end 

 separates from the basal part by an irregular 

 transverse line. The upper part of the cap- 

 sule, together with the style, comes off as a 

 lid (Fig. 185), and the single seed escapes. The seeds are 

 kidney-shaped, and yelhnv, or mixed yellow and violet in 

 color. 



Pollination. — Red clover flowers are protandrous. The 

 work of Westgate and Coe establishes the fact that " red 

 clover flowers must be cross-pollinated in order to set seed 

 on a commercial basis." The pollen must come from a 

 separate plant, for even when taken from flowers of the same 

 plant, the percentage of seed set is very small. The bundjle- 

 bee (Bombus) is the most important insect visitor of the red 

 clover. It is capable of pollinating 30 to 35 flowers a minute. 

 Honey bees are also efiicient poUinators. When the bumble- 

 bee lights on the clover head and inserts its proboscis into 

 the staminal tube, its weight i)re.sses down on the keel and 



Fig. 

 Fruit of red 

 clover (Trifo- 

 lium pratense), 

 much enlarged. 



