Positive aberrations are rather rare, and are mostly restricted to a
greater density of the [139] pubescence in some hairy species, as in
_Galeopsis Ladanum canescens_, _Lotus corniculatus hirsutus_ and so on.
But _Veronica scutellata_ is smooth and has a pubescent variety, and
Cytisus prostratus and _C. spinescens_ are each recorded to have a
ciliate form.
Comparable with the occurrence and the lack of hairs, is the existence
or deficiency of the glaucous effect in leaves, as is well known in the
common _Ricinus_. Here the glaucous appearance is due to wax distributed
in fine particles over the surface of the leaves, and in the green
variety this wax is lacking. Other instances could be given as in the
green varieties of _Papaver alpinum_ and _Rumex scutatus_. No positive
instances are recorded in this case.
Spines and prickles may often disappear and give rise to unarmed and
defenceless types. Of the thorn-apples both species, the whiteflowered
_Datura Stramonium_ and the purple _D. Tatula_ have such varieties.
Spinach has a variety called the "Dutch," which lacks the prickles of
the fruit; it is a very old form and absolutely constant, as are also
the thornless thorn-apples. Last year a very curious instance of a
partial loss of prickles was discovered by Mr. Cockerell of East Las
Vegas in New Mexico.
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