W THE SPECIES Or PRIMULA. 85 



ive agency already at work wliicli would have carried pollen from 

 one sex to the other. 



"What insects habitually visit Cowslips, as is absolutely necessary 

 for their regular fertility, I do not know. I have often watched 

 them, but perhaps not long enough ; and only four times I have 

 seen Humble-bees visiting them. One of these bees was gathering 

 poUeu from short-styled flowers alone, another had bitten holes 

 through the corolla ; and neither of these would have been effective 

 in the act of fertilization : two others were sucking long-styled 

 plants. I have watched Primroses more attentively during several 

 years, and have never seen an insect visit tliem ; yet from their close 

 similaritj' in all essential respects to Cowslips, there can hardly be 

 a doubt that they require the visits of insects. Hence I am led 

 to suppose that both Primroses and Cowslips are visited by motlis. 

 All the species which I- have examined secrete plenty of nectar. 



In Primula Sinensis, when protected from insects and not arti- 

 ficially fertilized, tiie case is somewhat, but not materially, different. 

 Five short-styled plants produced up to a given period 116 flowers, 

 which set only seven capsules, whereas twelve other flowers on 

 the same plants artificially fertilized set ten capsules. Five long- 

 styled plants produced 147 flowers, and set sixty-two capsules ; so 

 that this form, relatively to the other, sets afar greater number of 

 capsules : yet the long-styled protected flowers do not set nearly 

 so well as when artificially fertilized ; for out of forty-four flowers 

 thus treated, thirtj'-eight set. These remarks apply only to the 

 early setting of tlie capsules, many of which did not continue 

 swelling. With respect to the product of seed, seven protected 

 short-styled plants, which bore about 160 flowers, produced only 

 lialf a grain of seed ; they ought to have produced 120 grains : so 

 that the short-styled plants, when protected from insects, are nearly 

 as sterile as Cowslips. Thirteen long- styled plants, which bore 

 about 380 flowers, and which as we have seen set many more cap- 

 sules, produced 25'9 grains of seed ; they ouglit to have produced 

 about 220 grains in weight': so that although far less fertile tlian 

 the artificially fertilized flowers, yet the long-styled P. Sinensis, 

 w'hen protected from insects, is nearly twenty-four times as fertile 

 as the short-styled when protected from insects. The cause of 

 this difference is, that when the corolla of the long styled plants 

 falls oflf, the short stamens near the bottom of the tube are neces- 

 sarily dragged over the stigma and leave pollen on it, as I saw by 

 hastening the fall of nearly withered flowers ; whereas in the short- 

 styled flowers, the stamens are seated at the mouth of the corolla, 



