THE GENUS ROSA 27 1 



diverse ways by insect visitors. Firstly, every flower bears 

 its own colony of the widely distributed Taeniothrips primulce 

 — an insect, contrary to the indications of its name, very 

 impartial in its predilections. This Thrips rarely leaves its 

 own particular flower, but spends its time in wandering indis- 

 criminately amidst stigmas and anthers, and thus unavoidably 

 carries pollen from the latter to the former. Secondly, insects 

 from elsewhere, whilst in some measure rendering cross- 

 pollination possible, since they are always pollen eaters and 

 not nectar* gatherers, crawl at random from anther to anther, 

 touching the stigmas as they pass, and deposit strange as well 

 as adjacent pollen with the same result as before. Thus, to a 

 very unexpected degree, the roses prove autogamous ; that 

 cross-pollination can occur, and in a manner likely to secure 

 hybridity, the following journeys of the bees Botnbns pratorum 

 and Andrena trimmerana will give adequate proof. 



(i) Journey of a worker Bombus pratorum: — Rosa mollis 

 var. caerulea, R. pimpinellifolia^ R. oinissa. 



(2) Journey of a second worker B. pratorum: — R. mollis 

 type, R. mollis var. caerulea. 



(3) Journey of a female Andrena trimmerana: — R. pim- 

 pinellifolia, R. mollis var. caerulea, R. mollis type, Saxifraga 

 lingulata, Rubus idceus, Aquilegia canadensis. 



How generously the roses are patronised by insects, and 

 therefore some degree of cross-pollination possible, can be 

 determined from the table on pages 272 and 273. 



With such a crowd of guests as this, and guests of such 

 cosmopolitan tastes, could one be surprised, even where 

 autogamy and apomixis to a greater or less extent prevail, if 

 hybridity became exceedingly frequent? 



Cleistogamy. 



In such a genus as Rosa one would scarcely anticipate the 

 occurrence of cleistogamous flowers, so little need does there 



* Unless the shining secretion on the exposed disk of the Eucanincs, 

 Agrestcs and Tomentosa is nectar the Rosa do not secrete that substance. 



