PART IIL. ] THE MECHANISMS OF FLOWERS. 105 
Nasturtium officinale, though the number of glands is as in N. 
silvestre (590, I.). 
31. DRABA VERNA, L.—Four small, green, fleshy honey-glands 
occur in each flower, each being situated between the bases of a 
short stamen and the long one next it; so that the base of each 
short stamen stands between two honey-glands. Anthers and 
_ stigma ripen together. The longer stamens reach to a level with 
_ the stigma, and stand close around it: they dehisce on those sides 
_ which are turned towards the stigma, and always dust it with 
| pollen; the shorter stamens also turn their pollen-covered surfaces 
| towards the stigma, but stand below it. Honey-seeking insects 
_ must thrust their proboscides between the stigma and one of the 
_ shorter stamens into the base of the flower, and so dust themselves 
_ with pollen, especially from the shorter stamens, and carry it 
_ elsewhere, Cross-fertilisation is chiefly effected with pollen from | 
_ the shorter stamens, while the four longer ones regularly effect self- 
fertilisation. Hildebrand has found by experiment that the latter 
is productive. We may understand the extensive use that this 
plant makes of self-fertilisation if we consider how small and 
_ inconspicuous the flowers are, how small a supply of pollen or 
honey they can yield, and how few insects they are for these reasons 
visited by. I have only observed three species of bees on Draba 
verna, VIZ :— 
, (1) Apis mellifica, L. §, cp. (April 10, 1868); (2) Andrena parvula, K. 
 ¢,. (March 28, 1869) ; (3) Halictus sp. 9, s. (March 28, 1869). 
Draba aizoides, L., is proterogynous with persistent stigmas (600). 
Draba Wahlenbergii, Hartm., is homogamous (609). 
32. COCHLEARIA OFFICINALIS, L.—Near Niederalma, I saw the 
following insects on flowers of this plant (July 12, 1869) :— 
A. Diptera—Syrphide : (1) Eristalis tenax, L.; (2) Helophilus floreus, 
_ L.; (8) Melanostoma mellina, L., ab., all three both s. andc.p. B. Coleoptera 
_ —(4) Cetonia aurata, L., gnawing the parts of the flower. 
Kernera saxatilis, Rich., is homogamous. The four longer 
stamens bend laterally almost to a right angle, so that their anthers 
come to lie quite close to those of the shorter stamens (609). 
Thlaspi arvense, L., is homogamous. The shorter stamens are 
concerned in cross-fertilisation ; the longer, in case of need, effect 
self-fertilisation (590, I1.). 
