340 . DARWimANA. 



natural if less useful state, its hold on life would evi- 

 dently be increased rather than diminished. 



As to natural varieties or races under normal con- 

 ditions, sexually propagated, it could readily be shov^n 

 that they are neither more nor less likely to disappear 

 from any inherent cause than the species from which 

 they originated. Whether species wear out, i. e., have 

 their rise, culmination, and decline, from any inherent 

 cause, is wholly a geological and very speculative prob- 

 lem, upon which, indeed, only vague conjectures can 

 be offered. The matter actually under discussion con- 

 cerns cultivated domesticated varieties only, and, as to 

 plants, is covered by two questions. 



First, Will races projpagated hy seed, being so fixed 

 that they come true to seed, and purely bred (not 

 crossed Avith any other sort), continue so indefinitely, 

 or will they run out in time — not die out, perhaps, 

 but lose their distinguishing characters ? Upon this, 

 all we are able to say is that we know no reason why 

 they should wear out or deteriorate from any inherent 

 cause. The transient existence or the deterioration 

 and disappearance of many such races are sufficiently 

 accounted for otherwise ; as in the case of extraordi- 

 narily exuberant varieties, such as mammoth fruits or 

 roots, by increased liability to disease, already adverted 

 to, or by the failure of the high feeding they demand. 

 A common cause, in ordinary cases, is cross-breeding, 

 through the agency of wind or insects, which is diflScult 

 to guard against. Or they go out of fashion and are 

 superseded by others thought to be better, and so the 

 old ones disappear. 



Or, finally, they may revert to an ancestral form. 



