flower, such species are excluded from the lists; as are likewise dimorphic and trimorphic plants, in which the same necessity occurs to a limited extent.  Experience has proved to me that, independently of the exclusion of insects, the seed-bearing power of a plant is not lessened by covering it while in flower under a thin net supported on a frame; and this might indeed have been inferred from the consideration of the two following lists, as they include a considerable number of species belonging to the same genera, some of which are quite sterile and others quite fertile when protected by a net from the access of insects.

[List of plants which, when insects are excluded, are either quite sterile, or produce, as far as I could judge, less than half the number of seeds produced by unprotected plants.

Passiflora alata, racemosa, coerulea, edulis, laurifolia, and some individuals of P. quadrangularis (Passifloraceae), are quite sterile under these conditions:  see ’Variation of Animals and Plants under Domestication’ chapter 17 2nd edition volume 2 page 118.

Viola canina (Violaceae).—­Perfect flowers quite sterile unless fertilised by bees, or artificially fertilised.

Viola tricolor.—­Sets very few and poor capsules.

Reseda odorata (Resedaceae).—­Some individuals quite sterile.

Reseda lutea.—­Some individuals produce very few and poor capsules.

Abutilon darwinii (Malvaceae).—­Quite sterile in Brazil:  see previous discussion on self-sterile plants.

Nymphaea (Nymphaeaceae).—­Professor Caspary informs me that some of the species are quite sterile if insects are excluded.

Euryale amazonica (Nymphaeaceae).—­Mr. J. Smith, of Kew, informs me that capsules from flowers left to themselves, and probably not visited by insects, contained from eight to fifteen seeds; those from flowers artificially fertilised with pollen from other flowers on the same plant contained from fifteen to thirty seeds; and that two flowers fertilised with pollen brought from another plant at Chatsworth contained respectively sixty and seventy-five seeds.  I have given these statements because Professor Caspary advances this plant as a case opposed to the doctrine of the necessity or advantage of cross-fertilisation:  see Sitzungsberichte der Phys.-okon.  Gesell.zu Konigsberg, B.6 page 20.)

Delphinium consolida (Ranunculaceae).—­Produces many capsules, but these contain only about half the number of seeds compared with capsules from flowers naturally fertilised by bees.

Eschscholtzia californica (Papaveraceae).—­Brazilian plants quite sterile:  English plants produce a few capsules.

Papaver vagum (Papaveraceae).—­In the early part of the summer produced very few capsules, and these contained very few seeds.