234 RECEPTION OF FLOWER-SEEKING ANIMALS AT THE FLOWER. 



plants. The flowers of Water-Lilies, of which the Victoria regia, represented 

 in Plate XI., may serve as type, the flowers and inflorescences of the Flowering 

 Rush (Butomus), of the Arrowhead (Sagittaria), of the ^^ater Plantain (Alisma), 

 of the Feather-foil (Hottonid), of Bladderwort (Utricularia), Villarsia (LimnMn- 

 themum), Frog-bit (Hydrocharis), Water Soldier (Stratiotes), and of many other 

 plants are amply protected by the belt of water which their situation involves. 

 Flies and beetles which come through the air for honey and pollen are welcome 

 visitors, promoting, as they do, a crossing of the pollen; snails, centipedes, &c. 

 are, on the other hand, kept back by the water. The basins of water formed 

 by the bases of the leaves in the Teasel (Dipsacus) and Sil/phimn perfoliatum 

 (figured, vol. i. p. 239), serve a like purpose, as also do the collections of water 

 in the funnel-like sheaths of the leaves of many Bromeliacese {jEchmea, Billbergia, 

 Lamprococcus, Tillandsia, &c.), though this is supplemented by other advantages 

 derived by these plants from the receptacles of water in question (c/. vol. i. 

 p. 241). 



More frequently even than by water the flowers obtain immunity from these 

 visitors by sticky secretions. The substance formed in many cases resembles 

 bird-lime in properties, though its chemical constitution is not fully ascertained; 

 in others it is allied to gum-arabic, or cherry-gum; whilst in others again it is 

 a resin or a mixture of resin and mucilage known by the name of gum -resin. 

 Occasionally this purpose is served by latex, which readily escapes from the 

 brittle tissues and coagulates on the surface into an adhesive substance. This 

 last method obtains particularly in certain Asclepiads, and in many species of 

 Lettuce (e.g. LoLctuca angustana, sativa, Scariola). The involucral scales which 

 inclose the flower-heads of these plants are smooth and tense, and abound in 

 latex. No obstacle prevents creeping insects, especially ants, from climbing up to 

 this point; but as soon as the ants reach these scales on their way to the flowers, 

 and touch the turgid investing cell -layers, they rupture the walls of the latex- 

 tubes (which in some cases actually project as tiny hairs on the surface) with 

 the claws of their feet, and the milk runs out in little droplets. Their feet and 

 abdomens are smeared with latex, and when the ant bites at the substance of 

 the scales in self-defence its head also becomes involved in the sticky mess. It 

 seeks to free itself of this encumbrance in a variety of ways, but the result of 

 all these struggles is merely a further rupturing of the epidermis and discharge 

 of latex, which adds to the embarrassment of the ant. Some of these creatures 

 manage to escape and drop to the ground, others, not so fortunate, are glued in 

 the coagulating latex, where their dead bodies may be seen decorating the involucre 

 of the capitulum. 



The other adhesive substances mentioned arise either from certain circum- 

 scribed cells of the flat epidermis of the stem, or else definite projecting structures 

 known as glands, glandular hairs, capitate hairs, &c., are specialized for this pur- 

 pose. In the case of flat epidermal cells, the secretion is passed out from the cells 

 and collects between the inner and outer layers of the external wall, in other words. 



