CHAP. X. PLANTS STERILE WITHOUT INSECT-AID. 363 



on the summits of three of the spikes, which touched the 

 net when the wind blew, produced a few seeds. This 

 sterility \vas not due to the injurious effects of the net, for I 

 fertilised five flowers with pollen from an adjoining plant, 

 and these all yielded fine seeds. I removed the net, whilst 

 one little branch still bore a few not completely faded 

 flowers, and these were visited by bees and yielded seeds. 

 8. coca'necr. Some covered-up plants produced a good many 

 fruits, but not, I think, half as many as did the uncovered 

 plants ; twenty-eight of the fruits spontaneously produced 

 by the protected plant contained on an average only 1 * 45 

 seeds, whilst some artificially self-fertilised fruits on the 

 same plant contained more than twice as many, viz., 3 3 



Bignonia (unnamed species) (Bignoniacese). Quite sterile : see 

 my account of self-sterile plants. 



Digitalis purpurea (Scrophulariacese). Extremely sterile, only a 

 few poor capsules being produced. 



Linaria vulgaris (Scrophulariaceae). Extremely sterile. 



Antirrhinum majus, red var. (Scrophulariacese). Fifty pods 

 gathered from a large plant under a net contained 9 8 grains 

 weight of seeds ; but many (unfortunately not counted) of 

 the fifty pods contained no seeds. Fifty pods on a plant 

 fully exposed to the visits of humble-bees contained 23 1 

 grains weight of seed, that is, more than twice the weight ; 

 but in this case again, several of the fifty pods contained no 



A. majus (white var., with a pink mouth to the corolla). 

 Fifty pods, of which only a very few were empty, on a 

 covered-up plant contained 20 grains weight of seed; so 

 that this variety seems to be much more self-fertile than 

 the previous one. With Dr. W. Ogle ('Pop. Science 

 Review,' Jan. 1870, p. 52) a plant of this species was much 

 more sterile when protected from insects than with me, for 

 it produced only two small capsules. As showing the 

 efficiency of bees, I may add that Mr. Crocker castrated some 

 young flowers and left them uncovered ; and these produced 

 as many seeds as the unmutilated flowers. 



A majus (peloric var.). This variety is quite fertile when arti- 

 ficially fertilised with its own pollen, but is utterly sterile 

 when left to itself and uncovered, as humble-bees cannot 

 crawl intc the narrow tubular flowers. 



