208 



POPULAR SCIENCE MONTHLY. 



pissadi), of which there was no other specimen in America, it was 

 grafted on to the Kelsey plum, a variety of Primus triflorus. The 

 graft itself did not bloom, but the presence of the graft brought about 

 in the tree a cross of the two species. This is the only case known to 

 me in which the graft affected the reproductive system of the plant, 

 forming a cross between forms which had never crossed. Many hun- 

 dred descendants of this cross are now living. Darwin accepted with 

 reservations the account of the graft hybrids in potatoes, and there still 

 remains some doubt of reliable testimony of the supposed fact. He 

 also speaks of a now well-known graft hybrid of a yellow and purple 

 cytisus, which is perhaps the most remarkable fact in this line on 

 record." 



Diagram showing the Zone of Life and Parallelism of 

 Results in Crossing and Grafting. (L. B.) 



Utter refusal to unite under any circumstances, either by crossing 

 or grafting. (Outside of zone of possible union. ) 



co 

 O 

 W 

 H 

 CO 



X 



pq 

 a 



M 



co 



CO 



o 



« 



Pollen acts as a poison. 



Union partial, mosaic or tem- 

 porary ; seed rarely produced ; 

 seedlings generally inherit tend- 

 encies and qualities of one pa- 

 rent only ; second or later gen- 

 erations revert fully. 



Union free ; seedlings show 

 unbalanced condition, varying 

 widely ; often unusually vigor- 

 ous ; best condition for scientific 

 or natural selection. Good qual- 

 ities can be made permanent to 

 the race. 



Unite freely ; seed of superior 

 germinating quality produced 

 abundantly. Seedlings normal 

 with ordinary amount of vari- 

 ability. 



Mendelian 



or 



Mutative 



State. 



Unusual 



Variation. 



Grafts blight and die as if 

 poisoned. 



Grafts often form a temporary 

 union but are not in a normal 

 condition. Avoided by nursery- 

 men and planters with great 

 care, as results are often disas- 

 trous to the grower. 



Grafts unite readily but sepa- 

 rate under unusual stress — 

 drought, overbearing, lack of 

 nourishment, etc. Avoided by 

 nurserymen and planters. 



Grafts unite readily, thriving 

 well ; sometimes better than 

 when grafted on their own 

 stock. 



O 

 w 

 o 



to 



w 



I— I 



Q 



W 



Q 

 si 

 > 



Ordinary plant life as oftenest 

 met with. 



Normal. Grafts unite and thrive as we 



oftenest see them. 



Self-fertile ; seed produced, 

 but as there are very limited 

 opportunities for profitable vari- 

 ations, this state ultimately ends 

 in 



Grafts grow on their own 

 roots. 



Extinction. 



All these varying states shade off from one to the other, with few hard and fast 

 lines of separation. 



