140 Shaw — Structure of the F/cnvers in 



Nectary. — No indication of a nectary has been observeci in 

 the cleistogamic flowers. 



In P. paiicifolia no intermediate types of flower have as yet 

 been found. It is possible, however, that a more extensive 

 search in its native habitat would reveal the existence of such. 



Such studies as these must inevitably raise the inquiry, 

 " Why are cleistogamic flowers developed, and what purpose 

 do they serve in the history of the plant ? " Many investiga- 

 tors have studied cleistogamic flowers and several explanations 

 have been ofiered. 



The existence of minute, self-fertilized flowers has been 

 known for several centuries. The first satisfactory descrip- 

 tion of them was given in 1857 t>y Dr. Miiller, of Upsala,' 

 who described the apetalous flowers of Mola canina. In 

 1863 Hugo von Mohl - published further observations with 

 the history of the subject. In i S67 Dr. Kuhn ' gave to such 

 flowers the fitting term " cleistogamic." 



We may now review the various opinions which have been 

 held concerning the cause and meaning of these. 



Delpino ^ believed that cleistogamic flowers have been 

 developed in order to ensure the production of seeds under 

 climatic or other conditions, which tend to prevent the fertili- 

 zation of the perfect flowers. Axell ^ supposed similarly that 

 the existence of cleistogamic flowers was due partly to low 

 temperature, which hindered the development of ordinary 

 flowers, and partly to failure of insects which, under normal 

 circumstances, effect cross fertilization. Fritz Miiller, in much 

 the same way, believed that cleistogamy was to preserve the 



' Botanische Zeitung, 1857, p. 730. 

 '^ Ibid., 1S63, pp. 307-28. 

 ^ Ibid., 1S67, p. 65, 



« " Sulla Opera la Distribuzione del Sessi nelle Plante," 1867, p. 30. 

 5 " Severin Axell," Om an ordniugama for fanerogama vaxtemas befrukting. 

 Stockholm, 1869. 



