PLANT HYBRIDIZATION BEFORE MENDEL 229 



which are so far from being sterile that their fertility is often actually 

 augmented, have, as previously shown, their size, hardiness, and constitu- 

 tional vigour generally increased. It is not a little remarkable that an 

 accession of vigour and size should thus arise under the opposite contin- 

 gencies of increased and diminished fertility," (ic, 2: 108.) 



In the case of Darwin's experiments to determine the relative 

 effects upon vigor of selling and crossing, respectively, the data 

 were determined chiefly with respect to height and weight of the 

 plants, which were grown on opposite sides of the same pot in 

 all instances. 



Regarding the relative heights and weights of 292 plants de- 

 rived from a cross with a fresh stock, and of 305 plants either 

 selfed or intercrossed between plants of the same stock, and be- 

 longing to thirteen species and twelve genera, Darwin says : 



"Considering all the cases . . . there can be no doubt that plants profit 

 immensely, though in different ways, by a cross with a fresh stock, or 

 with a distinct sub-variety." He emphasizes further, "it cannot be main- 

 tained that the benefit thus derived is due merely to the plants of the 

 fresh stock being perfectly healthy, whilst those which had been long 

 intercrossed or self-fertilized had become unhealthy; for in most cases 

 there was no appearance of such unhealthiness." {ib., p. 269.) 



Experiments were also made with plants belonging to five 

 genera in four different families. One of the most interesting 

 cases was that of a plant of marjoram (^Origanum vulgar e). The 

 height of the crossed was to that of the selfed as 100 : 86. 



"They differed also to a wonderful degree in constitutional vigour. 

 The crossed plants flowered first, and produced twice as many flower- 

 stems; and they afterwards increased by stolons to such an extent as 

 almost to overwhelm the self-fertilized plants." (lb, p. 302.) 



Darwin holds that the inferiority of the selfed seedlings in 

 height can have been in no way due to any morbidity or disease 

 in the mother plants ; certainly, he maintains, no such theory of 

 a diseased condition would in anywise hold, in the case of 



". . . intercrossing the individuals of the same variety or distinct va- 

 rieties, if these have been subjected durilig some generations to different 

 conditions." (lb, p. 450.) 



In four out of the five cases experimented with, the intercrossing 

 of flowers upon the same plant did not differ in effect from the 

 strictest self-fertilization. He says : 



"On the whole, the results here arrived at . . . agree well with our 

 general conclusion that the advantage of a cross depends on the progeni- 

 tors of the crossed plants possessing somewhat different constitutions, 



