IMPERFECTION OF POLLEN AND MUTABILITY IN 



THE GENUS ROSA* 



Ruth D . Cole 



During the winter 



(with plates iv-vi) 

 of 1915-1916 I made a study of all the 



hich specimens 



6 



This was done in connection with work on other genera of the family 

 Rosaceae, notably on Rubus and on Crataegus; and it has been 

 interesting to note that in all 3 genera there is indication of a large 

 amount of hybridism, and that the multiplication of species is 

 startlingly great. 



From the Arnold Arboretum of Harvard 



I have 



been able to obtain flower buds of 32 different species of Rosa. 



sissima, 3 of R. rugosa, and 2 of R. virginiana. 

 taken when on the point of opening, thus ma 



spino 



buds 



maturity 



tking sure of the 

 They were then preserved in alcohol until 



time as it was possible to examine them 



I prepared sections of about half of the species gathered, with 

 iew to determining how many showed sound pollen and how 



many 

 imDer 



parts. 



set pollen. For this purpose the buds were first imbedded 

 >idin to make sure that there would be no shrinkage of the 

 Sections were cut with the microtome, stained with Heiden- 

 haematoxylin and safranin, and finally mounted in balsam. 

 ' nearly a century it has been known that one of the most 



important and most 

 is imDerfect Dollen. 



>erfect pollen. Dutrochet 1 in 1832 recognized the morpho- 

 logical sterility of the hybrid and pointed out that pollen abortion 

 is a criterion for hybridism. Gaertner, 2 in 1849, speaks of the 



*Contribution from the Laboratories of Plant Morphology of Harvard University. 



trochet, Henri 



Gard. Mag. 8:500. 1832. 



im 



Pflanzenreich. Stuttgart. 1849. 

 Botanical Gazette, vol. 63] 



[no 



