Discusses differences between Asa Gray’s view and his own on crossing. A common effect is the obliteration of incipient varieties. There is heavy evidence against new characters arising from crossing wild forms, "only intermediate races are then produced". Innate vital forces are somehow led to act differently as a result of direct effect of physical conditions. Astonished by JDH’s statement that every difference might have occurred without selection. CD agrees, but JDH’s manner of putting it astonished him. CD says, "think of each of a thousand seeds bringing forth its plant, and then each a thousand … I cannot even grapple with idea". Responds to JDH’s and Lyell’s feeling that he made too much of a deus ex machina out of natural selection. [Letter actually dated 20 Nov but is certainly after 3831.] [wrong field?]