CHAP. VIII. ON CLEISTOGAMIC FLOWERS. 343 



pear. The result would be the production of cleisto- 

 gamic flowers such as we now see them; and these are 

 admirably fitted to yield a copious supply of seed at a 

 wonderfully small cost to the plant. 



I wilt now sum up very briefly the chie'f conclusions 

 which seem to follow from the observations given in 

 this volume. Cleistogamic flowers afford, as just stated, 

 an abundant supply of seeds with little expenditure; 

 and we can hardly doubt that they have had their struc- 

 ture modified and degraded for this special purpose; 

 perfect flowers being still almost always produced so 

 as to allow of occasional cross-fertilisation. Herma- 

 phrodite plants have often been rendered monoecious, 

 dioecious or polygamous; but as the separation of the 

 sexes would have been injurious, had not pollen been al- 

 ready transported habitually by insects, or by the wind 

 from flower to flower, we may assume that the process 

 of separation did not commence and was not completed 

 for the sake of the advantages to be gained from cross- 

 fertilisation. The sole motive for the separation of the 

 sexes which occurs to me, is that the production of a 

 great number of seeds might become superfluous to a 

 plant under changed conditions of life; and it might 

 then be highly beneficial to it that the same flower or 

 the same individual should not have its vital powers 

 taxed, under the struggle for life to which all organisms 

 are subjected, by producing both pollen and seeds. 

 With respect to the plants belonging to the gyno-dice- 

 cious sub-class, or those which co-exist as hermaphrodites 

 and females, it has been proved that they yield a much 

 larger supply of seeds than they would have done if 

 they had all remained hermaphrodites ; and we may feel 

 sure from the large number of seeds produced by many 

 plants that such production is often necessary or ad- 



