15a1

Natural selection, p. 102

Categories of Species

Plants distinguishable from each other by positive characters, & generally received as true Species.
Same as No 1; but so closely resembling each other as to be frequently mistaken one for the other, & by botanists even of some experience.

Natural selection, p. 102

3. Same as No 1; & not liable to be mistaken in their typical forms; but accompanied by intermediate or transition forms, approximating so much to each or both, as not to be quite satisfactorily assigned to either. (N.B. The primrose & cowslip would be in this category, but it has been there proved that the intermediate produces both the alleged species from the same year's seed)/

15a2

Natural selection, p. 103

Plants deemed true species where their typical & most general forms only are looked at; but the limit of the species is rendered uncertain by the existence of forms closely allied, deemed varieties of the type by some botanists, distinct species by other botanists. As is the case with the intermediates of no. 3, so these varieties or sub-species of No 4 are usually much more rare or local than the type species. They differ from the intermediates of No 3 only as varieties or quasi species clustering around one, instead of uniting together two supposed genuine species./

15a3

Natural selection, p. 103

Altho' four such categories are easily defined on paper, & illustrated by selected examples, they glide together by other examples; & thus, as groups, they are different in degree rather than in kind. To give examples of the four categories,
1. The Apricot, plum, & Cherry are commonly placed under one genus, Prunus; & as species these are very readily distinguished by any body.

2. But there are two Cherries spontaneous in England, an arborescent & a fruticose, which by most botanists are deemed two real though very similar species, & between which in a wild state we can hardly point out any connecting links./

15a4

Natural selection, p. 103

Many botanists deem the wild sloe of England to be quite a distinct species from the cultivated & probably imported plum-tree of the gardens. Nevertheless, between the plum-tree of the garden & the sloe-bush of the hedges, there exist numerous intermediate forms or links, which render it highly difficult to say, 'here ends the sloe & its varieties, there begins the plum & its varieties I If we hold the intermediate Bullace a good species, this also passes insensibly down to the sloe, & improves almost as insensibly into the plum, so numerous & fine are the steps or links either way.

4. Linne described the fruticose bramble as a species, under name of Rubus fruticosus; but various modern botanists make out 50 to 100 supposed species of Bramble which others call varieties of R. fruticosus, & others again group into a small number of species, say half a dozen./