PEOPAOATION BY DIVISION NOT A CAUSE OF DEBILITY. 269 



object the increase of a given race. There is, however, this 

 very important difference, that while eyes multiply the 

 individual, seeds only multiply the species. 



For example the Grreen Gage Plum, ig a variety of the species Prunug 

 domestica. The seed of a Green Gage will undoubtedly produce Prunus 

 domestioa, tut not a Green Gage. On the other hand an eye (cutting or 

 graft) of the Green Gage Plum will increase that particular variety. 



" Although it occasionally happens that some one branch of a plant 

 disagrees from the rest of the branches in certain small peculiarities of 

 growth, such as the colour of the leaves, the doubleness of the flowers, 

 the character of the fruit, &c., thus acquiring the properties of a special 

 variety, yet this is an exception to rule. Every part detached from 

 a plant continues to correspond with its parent after its separation, and 

 for this reason propagation by division affords the means of mvdtiplying 

 varieties which either could not be propagated at all by seed, or only 

 with uncertainty.'' MoM. 



It has, however, been generally asserted that varieties 

 multiplied for many generations by eyes (cuttings or grafts) 

 gradually degenerate, become diseased, and disappear ; whence 

 it is said that propagation by eyes can only be employed with 

 safety for a few generations. For this idea there seems to be 

 no sufficient foundation ; but as it will be further examined in 

 Chapter XVII., I content myself for the present with quoting 

 the opinion upon the subject of Prof Mohl, the greatest of 

 modem German physiologists. " Thousands of experiments," 

 he observes, " have shown that the young shoots of old trees, 

 when used as grafts, slips, &c., furnish as strong plants as the 

 shoots of young trees. Even in the Palms (Phoenix dactylifera) 

 experiment has proved that the apex of the stem, when its 

 vegetation begins to slacken in an old tree, grows again into a 

 strong tree when cut off and planted in the earth. Not one 

 single experiment speaks in favour of the opinion promulgated 

 by Knight, that all parts of a tree have a common end to their 

 life, and that the different trees which have been raised from 

 one and the same tree by grafts, decay about the same time as 

 the parent plant. A whole series of cultivated plants (I will 

 only mention the Vine, the Hop, the Italian Poplar, and the 

 Weeping Willow) are propagated by division, without any 



