92 
FLOWERS AND INSECTS 
Gentians, Ericas, Primulas, &c., a long tubular gamopetalous 
corolla. 
Most of the flowers so far considered have radial symmetry, 
and stand more or less erect. When zygomorphism occurs, 
or a hanging or horizontal position of the flower, or special 
concealment of the honey in any way, as in many Legumi- 
nosae, Orchidaceae, &c., it is found that the flowers are 
chiefly visited by long-tongued bees, which are almost the 
only insects clever enough to obtain the honey in such cases. 
The length of tube is usually 6 — 15 mm., or that of bees’ 
tongues ; the flowers are visited chiefly by long-tongued bees 
and form the class H (“bee-flowers”). 
Whilst, as we have said, most flowers are visited by all 
the insects best suited to them and have therefore a consi- 
derable variety of visitors, there are numerous cases of more 
special restriction. Thus the carrion smell and appearance 
of the flowers of Rafflesia, Stapelia, Ceropegia, Aristolochia, 
Arum, Helicodiceros and many others cause them to be 
visited only by carrion-loving (short-tongued) flies ; they form 
a sub-class “carrion-fly flowers.” The flowers of Epipactis, 
Scrophularia, Symphoricarpus, Cotoneaster, &c. are “wasp- 
flowers.” A number of flowers of class F, e.g. Silene nodiflora , 
Oenothera binnis , Nicotiana tabacurn , &c., emit their scent 
only at night, thus attracting night-flying moths. Some of 
these, and Cereus, &c. only open at night. Such flowers have 
usually light yellow or white colours. Lastly, mention may 
be made of the very special mutual adaptation seen in Yucca, 
Ficus, Angraecum, &c. 
Many flowers of high type, with honey at the base of the 
tube, have their arrangements vitiated by the habit which 
certain humble-bees (especially Bombus terrestris) have of 
boring holes in the tube, and thus obtaining the honey 
without pollinating the flowers. Most flowers of the common 
bell-heathers (Erica) show a perforation at the base of the 
corolla thus made. If only humble-bees used it, the loss 
would not be so great, but it is used by hive-bees and wasps 
also, which do not bore the flowers themselves or only rarely. 
Other flowers that are often bored by Bombus are Aconitum, 
Dicentra, Lamium, Linaria, Nepeta, Salvia, &c. 
If in any locality the insect visitors to all the flowers be observed, 
and the number of species of each group visiting all the flowers of each 
