6 
POPULAR SCIENCE REVIEW. 
crossing, though all can probably fertilise themselves by their 
longer stamens. Small and inconspicuously flowering species 
are probably in all cases regularly self-fertilised, while some, as 
Shepherd’s-purse, are most abundant and vigorous. The stigmas 
of these are not two-lobed, but capitate (fig. 1). 
V iolaceas. — The genus Viola furnishes remarkable cases. 
The conspicuous flowers of the sweet Violet, adapted to insects, 
often fail to set seed ; but the cleistogamous buds seed profusely. 
These are degraded buds of the ordinary kind, for in strong 
growing garden plants transitions can be found, as shown in 
fig. 4, which represents a bud with the calyx removed. Fig. 
5 is a spurred petal, and fig. 6 a stamen with the appen- 
dage from another bud ; but neither the spur nor the nectary 
are now of any use. Fig. 7 is the pistil with its curved style, 
upon which the anthers are pressed. Fig. 8 shows the rudi- 
mentary petals of a wild cleistogamous bud of Violet. Fig. 9 
is a stamen. Fig. 10 is the pistil, the ovary of which 
after fertilisation swells and elevates the stamens, which re- 
main clinging to the summit. Fig. 11 is the pistil with the 
anthers removed, showing the curved style. 
Viola tricolor has not cleistogamous buds, but self-fertilising 
“forms ” instead. H. Muller has described onej form.* Fig. 13 
represents a form of var. arvensis which I found having a 
peculiar development of the placenta. It formed a pillar-like 
process, which rose up from the “throat” fig. 14 and pro- 
truded from the orifice in the globular “ head.” Pollen-tubes 
penetrated the centre of the pillar in abundance. Fig. 15 is 
another form, in which the placentiferous process was lengthened 
out over the “ lip,” and resembled a long tongue, which thus 
licked up the pollen from the calcarate petal. 
PoLYGALACEiE. — Polygala , though clearly adapted to cross- 
fertilisation, is yet often self-fertilised. The anther cells grip 
the spoon-like process on either side, and pour their pollen into 
it ; then the stigma becomes pollinated by bending back upon it 
according to Hildebrand, from whom fig. 17 is taken. In one 
form which I found, the anthers were on an exact level with the 
stigma, so that the pollen tubes were penetrating it from 
either side (fig. 18). 
CaryophyllacejE. — This order supplies many “weeds,” and 
weeds are mostly self-fertilising. Fig. 19 represents a bud of 
Spergula arvensis , which remained quite closed (in January), 
but was seeding freely all the while. Fig. 20 is the same with 
the calyx and corolla removed. Chickweed behaves in the same 
way (fig. 21). Both of these, like Shepherd’s-purse, will 
blossom and fruit all the year round as long as the weather wiP 
See i( Nature/’ Nov. 20, 1873. 
