38 AMBEICAN POMOLOGY. 



therefore, if one is an earlier sort than the other, it must 

 be retarded by shading or brought into a cooler situation, 

 and the latest forwarded by a warm wall or a sunny posi- 

 tion, so as to procure the desired result." 



We must distinguish between hybrids proper and crosses, 

 as it were between races or between what may have been 

 M-roneously designated species, for there has been a great 

 deal of looseness in the manner of using these terms by 

 some .writers. A true hybrid*' is produced only when the 

 pollen of one species has been used to fertilize the ovules 

 of another, and as a general rule these can only be pro- 

 duced between plants which are very nearly allied, as be- 

 tween species of the same genus. Even such as these, 

 however, cannot always be hybridized, for we have never 

 found a mule or hybrid between the apple and pear, the 

 currant and gooseberry, nor between the raspberry and 

 blackberry, though each of these, respectively, appear to 

 be very nearly related, and they are all of the order 

 Itosacem. 



In hybrids there appears to be a mixture of the ele- 

 ments of each, and the characters of the mule or cross 

 will depend upon one or the other, which it will more 

 nearly resemble. True hybrids are mules or infertile, and 

 cannot be continued by seed, but must be propagated by 

 cuttings, or layers, or grafting. If not absolutely sterile 

 at first, tlicy become so in the course of the second or 

 third generation. This is proved by several of our flow- 

 ering plants that have been wonderfully varied by ingeni- 

 ous crossing of diflferent species. But it has been found 



* BiUfoiir's Manual. 



