EECENT OBSEEYATIONS ON THE EEETILISATION OF PLANTS. 347 
closed flowers, which appear towards the end of the summer, 
resemble much more closely the well-known spring flowers, 
which are in this case certainly fertile. 
In accordance with the ordinary practice of economy by 
nature, the amount of pollen in the “ cleistogamous ” is generally 
very much less than in the open flowers, since it has very little 
chance of being wasted. In the small flowers of Malpighiacese, 
Jussieu states that there are only a very few grains of pollen ; 
in those of the wood-sorrel, where twenty to thirty ovules have 
to be fertilised. Von Mohl gives the quantity as from one to 
two dozen grains in each anther-cell ; in Impatiens it is con- 
siderably larger, while in Viola the number of grains is very 
smaU. 
More detailed examination of these closed flowers in difl’erent 
plants will doubtless yield interesting and important results. 
EXPLANATION OF PLATE OIL 
Fig. 1. {a-d) Different stages in the development of the pistil and 
stamens of Malva sylvestris, (n) nectar-glands ; (e) mature 
pistil and stamens of Molva rotundifolia. 
„ 2. Dianthus deltoides : (a) open flower, the flrst row of five stamens 
developed ; (6, e) pistil, with the two stigmas closely rolled 
together, (w) nectar glands ; (d) pistil at a later stage, with 
the stigmas unrolled and receptive. 
„ 3. Foot of a butterfly with pollen-masses of Asclepias curassavica 
attached to it. 
„ 4. (o) Eight hind-leg of Prosopis variegata] (6) right hind-leg of 
Bomhus Scrimshiranus. 
„ 5. End of the proboscis of Eristalis tenax ; (a) closed, (5) open, to 
show the cross-bars (r) with which it is furnished. 
„ 6. Drosera rotundifolia ; (a) unopened flower, (6) pistil and one 
stamen from the same. 
„ 7. Cleistogamous flower of Viola canina] (a) external view of 
flower ; (6) the same opened, showing pistil and two stamens ; 
(c) anther, with the pollen-bags {n) j (d) pistil (st) the re- 
ceptive stigmatic surface. 
(Figs. 1-5 after H. Muller.) 
