IN THE SPECIES OF PBIMULA. 96 



not, as has sometimes been maintained, mere dissemination. The 

 whole subject is as yet hidden in darkness. 



I will now only add that cases of dimorphism, like that of Pri- 

 mula, seem to be far from rare in the vegetable kingdom, though 

 they have been little attended to. A large and important class of 

 analogous facts will probably soon be discovered. Professor Asa 

 Grray* informs me, that he and Dr. Torrey have described several 

 Eubiaceous genera, in which some plants have exserted stamens, 

 and others exserted pistils. " Mitchella offers an interesting in- 

 stance of this structure from its relationship, through Nertera, to 

 Coprosma, one of the few dioecious genera of Miihiacete, and in 

 which the stamens are elongated in the male flowers and the styles 

 in the females." The long-styled hermaphrodite ilowers of Mit- 

 chella would probably be found more productive of seed tlian the 

 short-styled ; in the same way, but in a reversed manner, as in 

 Primula, the short-styled flowers are more productive than the 

 long-styled ; from which fact I inferred that, if Primula were to 

 become dioecious, the females would have short pistils and the 

 males short stamens, these being the corresponding organs neces- 

 sary for a heteromorphic union with full fertility. In the dioBcious 

 Coprosma, on the other hand, the females have long pistils, and 

 the males have long stamens. These facts probably show us 

 the stages by which a dioecious condition has been acquired by 

 many plants. 



Prof. A. Gray also informs me that another Eubiaceous genus 

 {Knoxia) in India has been described by Dr. Wight, with a 

 similar structure ; and this, I am told, is the case with Cinchona. 

 Several species of North Amei-ican Plantago are dimorphic, as is 

 Phamnus lanceolatus, as far as its female organs are concerned. 

 In the BoraginecB, Dr. Torrey has observed a strongly marked in- 

 stance in Amsinckia spectahilis : in some dried flowers sent me by 

 Prof. Grray, I find tliat the pistil in the one form is more than 

 twice as long as in the other, with a corresponding difference in 

 the length of the stamens ; in the short -styled flowers the grains 

 of pollen, as in Primula, apparently are larger, in the proportion 

 of nine to seven, than in the long-styled flowers, which have the 

 short stamens ; but the difiference can hardly be determined with 

 safety in dried flowers. In Mertensia alpina, another member of 



* See also Prof. Asa Gray's 'Manual of the Botany of the >f . United States,' 

 1856, p. 171. For Plantago, see p. 269. 



