INTRODUCTION. 3 



to be heterostyled. Again, a species tending to become 

 dioacious, with the stamens reduced in some individuals 

 and with the pistils in others, often presents a decep- 

 tive appearance. Unless it be proved that one form 

 is fully fertile only when it is fertilised with pollen 

 from another form, we have not complete evidence 

 that the species is heterostyled. But when the pistils 

 and stamens differ in length in two or three sets of in- 

 dividuals, and this is accompanied by a difference in 

 'the size of the pollen-grains or in the state of the 

 stigma, we may infer with much safety that the species 

 is heterostyled. I have, however, occasionally trusted 

 to a difference between the two forms in the length 

 of the pistil alone, or in the length of the stigma 

 together with its more or less papillose condition; and 

 in one instance differences of this kind have been 

 proved by trials made on the fertility of the two forms, 

 to be sufficient evidence. 



The second sub-group, above referred to, consists of 

 hermaphrodite plants, which bear two kinds of flowers 

 the one perfect and fully expanded the other mi- 

 nute, completely closed, with the petals rudimentary, 

 often with some of the anthers aborted, and the re- 

 maining ones together with the stigmas much reduced 

 in size; yet these flowers are perfectly fertile. They 

 have been called by Dr. Kuhn * cleistogamic, and they 

 will be described in the last chapter of this volume. 

 They are manifestly adapted for self -fertilisation, which 



* 'Botanische Zeitung,' 1867, partakes of the nature of a mon- 



p. 65. Several plants are known strosity. All the flowers on the 



occasionally to produce flowers same plant are commonly affected 



destitute of a corolla ; but they in the same manner. Such cases, 



belong to a different class of though they have sometimes been 



cases from cleistogamic flowers, ranked as cleistogamic, do not 



This deficiency seems to result come within our present scope : 



from the conditions to which the see Dr. Maxwell Masters, ' Vege- 



plants have been subjected, and table Teratology,' 1869, p. 403. 



