CHAP. X. MEANS OF CROSS-FERTILISATION. 379 



open flowers might easily have been converted into 

 closed ones. The graduated steps by which this pro- 

 cess could have been effected may be seen at the 

 present time in Lathyrus nissolia, Biophytum sen- 

 sitivum, and several other plants. The answer to the 

 above question obviously is, that with permanently 

 closed flowers there could be no cross fertilisation. 



The frequency, almost regularity, with which pollen 

 is transported by insects from flower to flower, often 

 from a considerable distance, well deserves attention.* 

 This is best shown by the impossibility in many cases 

 of raising two varieties of the same species pure, if they 

 grow at all near together ; but to this subject I shall 

 presently return ; also by the many cases of hybrids 

 which have appeared spontaneously both in gardens and 

 a state of nature. With respect to the distance from 

 which pollen is often brought, no one who has had any 

 experience would expect to obtain pure cabbage-seed, 

 for instance, if a plant of another variety grew within 

 two or three hundred yards. An accurate observer, 

 the late Mr. Masters of Canterbury, assured me that 

 he once had his whole stock of seeds " seriously affected 

 with purple bastards," by some plants of purple kale 

 which flowered in a cottager's garden at the distance of 

 half a mile ; no other plant of this variety growing any 



* An experiment made by K61- wards he counted the seeds of 



reuter (' Fortsetsuug,' &c. 1763, both lots: the flowers which he 



p. 69) affords good evidence on had fertilised with such astonish- 



this head. Hibiscus vesicarius is ing care produced 11,237 seeds, 



strongly diohogamous, its pollen whilst those left to the insects 



being shed before the stigmas are produced 10,886 ; that is, a less 



mature. Kolreuter marked 310 number by only 351; and this 



flowers, and put pollen from small inferiority is fully accounted 



other flowers on their stigmas for by the insects not having 



every day, so that they were worked during some diys, when 



thoroughly fertilised ; and he left the weather was cold with son- 



the same number of other flowers tinued rain, 

 to the agency of insects. After- 



