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Make pollen of one var. of Cabbage prepotent over another or one var. of Verbascum slightly prepotent over another.

It may be in some cases incidental. But wherever a new species has arisen, there has not always been another (as in such case as change of our Race-horse from Arab): this is a difficulty. — So in case of 2 species developed in 2 distant quarters of world. —

Again how are Hybrids themselves rendered sterile: this must be incidental for I will never believe that nat. selection was so blundering as to make the offspring sterile, & not the parents: moreover relation of sterility of p two parents & Hybrid child not strictly correlated — N. B. we have sterility of another kind induced in neuter insect of several kinds─ We could on this view understand a sterility in vars. selected by Man. — Perhaps understand the extreme variability in degree of sterility of Species. —

[165v]

Gärtner verbascum case, & maize & Kölreuter Tobacco, must be correlation. — The case of Lobelia, Crinum, & Passiflora, shows that under culture the potentiality of pollen & stigma varies.

It might be correlation in some cases & selection in others: or increased by selection; but then the extreme degree of & increasing degree of sterility as shown by different genera never crossing must be wholly due to correlation. —

Mem. Reciprocal Union how could these be explained?

What is case of Linum; may these not be case with one form having being dimorphic & not another