pissadi), of which there was no other specimen in America, it was grafted on to the Kelsey plum, a variety of Prunus 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 hundred 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.)
| Pollen acts as a poison. | Grafts blight and die as if poisoned. | |||
| Union partial, mosaic or temporary; seed rarely produced; seedlings generally inherit tendencies and qualities of one parent only; second or later generations revert fully. | Grafts often form a temporary union but are not in a normal condition. Avoided by nurserymen and planters with great care, as results are often disastrous to the grower. | |||
| Union free; seedlings show unbalanced condition, varying widely; often unusually vigorous; best condition for scientific or natural selection. Good qualities can be made permanent to the race. | Mendelian or Mutative State. |
Grafts unite readily but separate under unusual stress—drought, overbearing, lack of nourishment, etc. Avoided by nurserymen and planters. | ||
| Unite freely; seed of superior germinating quality produced abundantly. Seedlings normal with ordinary amount of variability. | Unusual Variation. |
Grafts unite readily, thriving well; sometimes better than when grafted on their own stock. | ||
| 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 variations, 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.
