FLOWERS OF IMPA TIENS FULVA 17 5 



tion in " the production of a large supply of seeds with little consumption 

 of nutrient matter or expenditure of vital force. " Delpino explains 

 cleistogamous flowers as an adaptation to secure the production of 

 seed under favorable climatic conditions. Shaw, (45) after giving an 

 historical resume of the subject, places emphasis on the cleistogamy 

 as an adaptation to secure the rapid development of fruit. 



The explanation of cleistogamous flowers as stages of arrested 

 development has been ofi'ered by various authors since the phenomenon 

 has been an object of investigation. Gray^ (18) as long ago as 1849, re- 

 garded the cleistogamous flowers of Impatiens fulva as buds arrested at 

 an early stage. Darwin agrees in part with the arrested development 

 idea, but offers some objections to it which argue for his view noted 

 above. Since Darwin's time, the conditions which bring about the 

 arrest have been determined through a wide range of observation and 

 experiment by various investigators. Temperature, toxicity of soil 

 attacks of parasites, reduction of leafage, moisture and light have been 

 demonstrated to be associated with the production of cleistagamous 

 flowers. Goebel (17) finds that all of these conditions affect the produc- 

 tion of cleistogamous flowers through the unfavorable conditions of 

 nourishment. He regards the cleistogamous flowers as "Hemmungs- 

 bildungen" of the chasmogamous flowers to be explained solely on the 

 ground of nourishment. The occurrence of the arrest in all stages 

 adds weight to the view. From the smallest cleistogamous flower with 

 no resemblance to the evolved z}'gomorphic chasmogamous type, 

 gradations may be shown through various sizes and degrees of pseudo- 

 cleistogamous flowers to the type which Hansgirg (20) originally gave the 

 name pseudo-cleistogamous, a flower similar in every respect to the 

 chasmogamous flower, but failing to open before fertilization. It is 

 but a step more to include in the series those showy flowers which nor- 

 mally are self-fertilized without opening or even to the expanded self- 

 fertilized species. 



Burck (11) added a new thought to the investigation when he ascribed 

 the origin of cleistogamy to mutation. It is worth noting, with mutation 

 in mind, the variety of families in which cleistogamy is reported. The 

 list of families given by Knuth (26) in which cleistogamy occurs, shows a 

 range from some of the simplest to the most evolved flowers. Among the 

 Monocotyledons it occurs in the relatively simple Alismaceae, Buto- 

 maceae, Graminaceae, Pontederiaceae; in the more evolved Juncaceae 

 and Liliaceae; in the most evolved family, the Orchidaceae. Among 

 Dicotyledons, it occurs in the less evolved Caryophyllaceae and Portu- 



