Poly gal a polygama and P. paiiciflora. 145 



suggestion in this connection that the developing fruits from 

 the minute flowers require a great quantity of carbohydrates 

 and so hinder the development of fruit from the evident 

 flowers. Knuth^ reviews the opinions of several of these 

 observers and concludes that light is the important factor in 

 cleistogamy. It will be noticed that Darwin's suggestion 

 that they were developed as a means of economy, does not 

 appear in the modern views. 



Perhaps, therefore, the consensus of opinion at the present 

 time in regard to cleistogamic flowers may be fairly stated as 

 follows : They are caused primarily by deficiency in light, or 

 by other unfavorable conditions, and are to be regarded as 

 degenerate or imperfectly developed chasmogamic flowers. 

 They are of advantage to a plant in preserving the species 

 when ordinary fertilization fails, and in the fact that their 

 fruits are often developed underground where they are 

 protected. 



These views either as to causes, or the purpose of cleisto- 

 gamic flowers are not very satisfactory when applied to such 

 aerial ones as are borne by Polygala polygama. In the first 

 place these are produced in abundance in the open fields 

 under the sun of July and August. The plants which bear 

 them show every sign of health, vigor and normal develop- 

 ment. If indeed it may have been that lack of light induced 

 their development in the first instance, it is necessary to 

 assume that there is some other cause at work when we find 

 them developed under all circumstances, and under bright 

 sunlight. The view that they are for the purpose of preserv- 

 ing the plant w^hen unfavorable circumstances prevent crossing, 

 is also more or less unsatisfactory, for each summer the cleisto- 

 gamic flowers are produced in great profusion. One would 

 hardly suppose that the chasmogamic flowers habitually fail 

 to find the conditions to which they are adapted. The fact 



^ Knuth. Bliithenbiologie. 

 10 



