498 CEOSS-BEEEDING EXTEBMELT EASY. 



On the other hand, cross-hreeding will take place as readily 

 among plants as among animals, and it is difficult to estimate 

 the alteration which this process has really produced, although 

 unperceived by us, in the amelioration and alteration of long 

 cultivated plants. "We cannot reasonably doubt that a process 

 so simple as that of dusting the stigma of one plant with the 

 pollen of another, which must be continually happening in 

 our gardens, either through the agency of insects or the 

 currents in the air, and which, where it takes place between 

 two varieties allied to each other, must necessarily produce a 

 cross, — we cannot suppose, I say, that this occurs in our 

 crowded gardens and orchards at that time only when we per- 

 form it artificially. 



The operation itself, although so simple, consisting in 

 nothing more than applying the pollen of one plant to the stigma 

 of another, nevertheless requires to be guarded by some pre- 

 cautions. In the first place, it is requisite that the flower 

 whose stigma is to be fertilised should be deprived of its own 

 anthers before they burst, otherwise the stigma will be self- 

 impregnated, and although superfoetation is not impossible, 

 yet it is not likely to occur. Then, again, the application of 

 the stranger pollen should be made at the time when the 

 stigma is covered with its natural mucus ; if not, the pollen will 

 not act, either in consequence of the necessary lubrification of 

 itself being withheld, from the stigma being too young, or 

 because the stigma, from age, has lost its power of receiving 

 the action of the pollen. Neither should the stigma be in 

 any way injured after fertilisation has apparently taken place. 

 The art of fertilisation consists in the emission, by the 

 pollen, of certain tubes of microscopical tenuity, which 

 pass down the style, and eventually reach the young seed, 

 with which they come in contact; and, unless this contact 

 takes place, fertilisation misses. Now the transmission of the 

 pollen tubes from the stigma to the ovule, through the solid 

 style, is often very slow, sometimes occupying as much as a 

 month or six weeks, as in the Mistletoe. 



Gsertner's experiments lead him to these practical con- 

 clusions : — 1. The time when impregnation will take place is 



