CONTRIBUTIONS FROM THE WISLEY LABORATORY. 17 
the flowers, the visits of which are less constant, and which may in 
some cases be only accidental, but which certainly play some part in 
effecting cross-pollination, provided inter-planting of varieties flowering 
at the same time is practised. 
Possibly Wisley is favoured by the visits of more of these useful 
insects than are many gardens, surrounded as it is by woods and 
common land and pasture, but the insects mentioned as most active 
are likely to find a home near most gardens and orchards. Humble 
bees nest about tufts of grass and in hedge bottoms and the like, 
Andrena in paths and banks, and allied genera in hollow sticks ; the 
larvae of the hover flies of the genus Syrphus and several other genera 
feed on green flies on apples, currants, and a variety of other plants, 
while those of the genus Eristalis are common in foul water, puddles, 
gutters, and so on. The grubs of midges feed in a variety of places, 
especially in vegetable refuse and manure, where also many grubs of 
larger two- winged flies are to be found. It is therefore unlikely that 
the supply of these insects will be short owing to unsuitable breeding 
places for them. 
In one case we have found hive bees more efficient in carrying 
pollen than the other insects mentioned, for in a series of observations 
made by one of us on flowers from which the petals had been removed, 
hive bees were almost the only insect visitors. Where the petals have 
been blown off prematurely, as sometimes happens in high winds, if a 
calm follows, hive bees may still act as carriers of the remaining pollen 
to other varieties. 
Our observations are conclusive as to the effective work of insects 
other than hive bees in carrying apple pollen ; they are less conclusive 
with pears and plums. They need to be carried over a longer period, 
but so far as they go they indicate that hive bees and two-winged 
flies are the most frequent visitors to pear flowers, humble bees being 
met with less commonly. Plums are visited actively by all three 
groups, but midges are perhaps less frequent in their flowers than in 
those of apples and pears. 
Apart from the obvious utility of hive bees in providing honey, 
their presence would make cross-pollination doubly sure • but on 
occasions where the keeping of them is not consistent with the economic 
management of the orchard, the work of cross-pollination may safely 
be left to wild insects. 
VOL. XLVII. 
c 
