80 INTRODUCTION 
themum leucanthemum was visited by a small slug (Limax laevis A/i//.) which in wet 
weather discharged the task of pollination. In one small area Ludwig found this 
slug on hundreds of capitula, and it seemed as if the white ray-florets formed the 
attraction, as they were very greedily devoured by the visitors. Ludwig thus com- 
ments on this observation :—‘It proves that plants which lack the customary agents 
of pollination, when continuous rain occurs during the flowering season, and would 
otherwise produce no fruit, may find in slugs effective substitutes for insects, which 
are only active in dry weather.’ Other botanists have repeatedly observed that snails 
and slugs visit and pollinate flowers, e.g.:—Engler (‘ Monogr. Phanerog. auct. A. et 
Cas. de Candolle,” V, 2, p. 30) substantiates this for Anthurium coriaceum and 
A. martianum, as he observed small slugs visiting them in the aquarium of the Botanic 
Garden in Munich. Trelease (Amer, Nat., Boston, xiii, 1879), in North America, 
saw small snails carrying pollen about on Symplocarpus foetidus Sa/isd. 
(d) Plants with Insect-pollinated Flowers. Entomophilae (En). 
In his ‘Das entdeckte Geh.’ (pp. 9-21) Sprengel has set forth the essential 
characters of insect-pollinated plants (cf. p. 5). An exhaustive account is therefore 
superfluous, and having regard to the present state of our knowledge, it will only 
be necessary to emphasize the most important points. 
In contrast to the dusty pollen of wind-pollinated plants, for which the name 
‘flower dust’ is very appropriate, insect-pollinated flowers possess adhesive pollen. 
Its outer coat is beset with small spines, warts, pits, grooves, needle- or hair-like 
structures, in short, with numerous small processes by which its adhesion to the 
bodies of visitors is specially favoured. At times the pollen-cells are bound together 
by threads of a delicate sticky substance known as Viscién, by which adhesion is 
rendered still easier. Such threads of wiscéz occur, e.g. on the pollen-grains of 
Oenothera, Epilobium, and other Onagraceae, among species of Rhododendron, &c. 
The size of pollen-grains varies greatly. It is mostly given in micromillimetres 
(1 p=o0-001mm.). Thus, according to Kerner (‘Nat. Hist. Pl,’ Eng. Ed. 1, II, 
p- 97), the size in Myosotis alpestris is 0-0025-0-0034 mm., ‘in Mirabilis Jalapa 
0:22-0:25 mm., so that in the latter plant it isa hundredfold that of the former. The 
average size is about 25-100 p. 
The pollen of all flowering plants, hydrophilous forms alone excepted, is at once 
damaged by water. Kerner has paid special attention to the many ways in which 
pollen is protected. I therefore enumerate the protective arrangements as distin- 
guished by him (‘ Nat. Hist. Pl.,’ Eng. Ed. 1, II, pp. 104-29). 
1. The anthers are covered by a protective roof. This is effected in 
one of the following ways :— 
(z) Campanulate, urceolate, basin-shaped, or cup-shaped flowers, depending from 
curved stalks, e.g. species of Calluna, Vaccinium, Campanula, Pulmonaria, and Con- 
vallaria ; Atropa Belladonna ; species of Galanthus, Leucojum, and Fritillaria. 
(6) Curvature of the main floral axts; the flowers are thus inverted as before, 
so that the stamens are sheltered by the petals :—Berberis, Prunus Padus. 
(c) Zhe flowers or inflorescences bend over periodically, their stalks (or the elon- 
gated inferior ovaries) curving downwards at night and in bad weather, so that once 
