parr ut] § THE MECHANISMS OF FLOWERS. 121 
sn. stigma is protected by a lip-shaped valve; but the pollen 
is shed directly upon the insect’s proboscis or head, as in V. odorata. 
Visitors: A. Hymenoptera—Apid@ : (1) Bombus agrorum, F., 9,s._ B. 
_ Diptera—Bombylide: (2) Bombylius discolor, Mgn. s. C. Lepidoptera— 
- (3) Anthocharis cardamines, L., s. ; (4) Pieris brassicae, L.; (5) P. napi, L., s. ; 
(6) P. rape, L., s. ; (7) Rhodocera rhamni, L., s. 
49, VIOLA CANINA, L. :-— 
lq Visitors: A. Hymenoptera—Apide: (1) Bombus lapidarius, L. 9, s. ; 
(2) Osmia rufa, L. ¢, s.; (3) O. fusea, Chr. 9,8. B. Diptera—Bombylide : 
_ (4) Bombylius major, L.,s. C. Lepidoptera—Rhopalocera: (5) Pieris rape, 
© L.,s.; (6) P. napi, L., s. 
Cleistogamic flowers have been observed in many Violarice : in 
_ V. mirabilis, L., by Dillenius; in V. pinnata, L., and V. montana, 
_L,, by Linnzus; in V. elatior, Fr., V. pumila, var. lancifolia, Thor. ; 
i] Y. odorata, L., bid V. canina, L., by Daniel Miiller; in Somidtum, 
SS , by Bornouilli: I can add V. bicolor* to this list. In the 
/ summer of 1859, I gathered some plants of this species at 
 Ramsbeck Waterfall, and placed them in a plate with water under 
the shadow of a bush in my garden, to let the flowers expand ; the 
plants, which I watched daily, grew well, and though no flowers 
_ opened I obtained plenty of capsules with good seed. Cleistogamic 
- flowers have been seen by Mr. T. H. Corry in V. silvatica, Fries., 
and in V. stagnina, Kit.; they are rare in the latter. Bennett has 
observed cleistogamic flowers in Viola cucullata, Ait., V. silvatica, 
V. floribunda, and V. sagittata, Ait. (79). 
EVOLUTION OF COLOUR IN VIOLETS. 
Various facts show that the flowers of the Violet were originally 
yellow. 
The smallest, most short-spurred of our Violas is V. biflora, 
ae is visited by Diptera, and only exceptionally by short-lipped 
es; its flowers are yellow. The smallest-flowered form of 
_V. tricolor (var. arvensis) has whitish-yellow flowers. The large- 
ia flowered V. tricolor, var. alpestris, shows all stages in the passage 
; from yellow flowers to blue; many plants have flowers which are 
| gyellow throughout, in others the flowers are yellow when they 
1 VY. bicolor, Pursh., is a form of V. tricolor, var. arvensis.—Asa Gray, North 
| American Flora, 
