216 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
If, on the one hand, self-sterility is specially emphasised where extra- 
ordinarily vigorous asexual reproduction narrows down the likelihood of 
separate physiological individuals appearing, as in the case of Symphytwm 
bulbosum, which, by offsets and their distribution, overran the whole of 
my garden in a few years; on the other hand, it particularly occurs, or 
even arises anew, where, with perennial plants, the prospects of cross- 
pollination seem specially secure. 
Examples of this are seen in Hrodiwm macradenum, E. pimpinelli- 
folium, and others. Of the first, I had in my garden two very floriferous 
plants raised from seed, which were fully adapted for cross-pollination 
by insects * and bore seed. In 1881 one of these, being planted out 
earlier, flowered several weeks before the other. The numerous umbels 
which were developed at this time did not set a single seed, despite self and 
general pollination; whilst after the flowering of the other plants 
numerous flowers were xenogamously fertilised. When later one of the 
plants died, the other, it is true, flowered annually, and developed an 
extraordinary floriferousness (anthomania), but never produced another 
seed. 
Hrodium cicutariwm is self-fertile. The insect-flowering form of E. 
pimpinellifoliwm, with large flowers and distinct ‘“‘ path-finder,”’ presents, 
on the other hand, all stages to self-sterility, parallel with the perfec- 
tion of arrangements for xenogamy. ; 
More or less regular and effectual insect visits to the various stations 
appear also to be the cause of a self-sterile form being coexistent with a 
self-fertile one in the case of Daphne mezereuwm. For years I have had a 
self-sterile bush of this in my garden, which came from a station at which 
bees, Colias Rhamni, and other insects were plentiful. So long as a 
second example of different origin grew in the vicinity, both bore and 
ripened annually numerous berries. In 1889 the companion plant died, 
and since then not a single fruit have I obtained, notwithstanding that 
microscopically the pollen is seen to be unaltered, and natural and arti- 
ficial pollination occurred among the flowers of the same stock. Twice, 
with years intervening, have I brought fresh blooming branches of 
Daphne from the wood into the vicinity, so that the numerous insects 
might carry foreign pollen to the plant. The result was what I ex- 
pected. The self-sterile example of Daphne set its berries, and developed 
them further until I removed them. In the years intervening, and after- 
wards, the tree remained perfectly barren until its death. Schulz found 
in Thuringia Daphne mezerewm self-fertile, and I myself have now a self- 
fertile plant in cultivation obtained from stations where insects are absent 
or scarce. It appears to me that an example of a step towards self-sterility 
is seen in a plant of Helleborus fatidws obtajned from Vernayaz, near St. 
Maurice, and possessing effective flowering arrangements. The two fruits, 
however, form no seed capable of germination; whilst examples less well 
adapted for insect fertilisation, from the Rhone Alps in Germany, form 
perfect seed. I have also in this case, for the continuance of the species, 
planted examples of both origins amongst each other. 
In conclusion, we may summarise the opinions at which we have 
arrived in a few short sentences. 
* See my work, “ Kosmos IV.,’’ Heft 11, Bot. Centralblatt, 1881, vol. v. p. 298. 
