TAKING UP OF POLLEN BY INSECTS. 243 



protecting flowers. We have already seen how ants are diverted from visiting 

 flowers by honey secreted on the foliage, and how, in certain instances, an actual 

 symbiosis obtains between the plant and the ants. Especially do these ants 

 protect the foliage from the attacks of leaf-eating animals. This reciprocal service, 

 performed by the ants, is in no wise of the nature of gratuitous philanthropy, 

 it is done in their own interests. The lodging and the food which the ants obtain 

 from the plant constitute two of their most important necessities, consequently it 

 is worth their while to protect the " goose that lays the golden eggs ". 



A similar state of afiairs is met with on the capitula of several Composites 

 indigenous to South-eastern Europe, e.g. Centaurea alpina and RutJtenica, Jurinea 

 TYiollis, and Serratula lycopifolia — the last of which is figured opposite. The young 

 capitula of these Composites are particularly liable to the attacks of devouring 

 beetles, especially of Oxythyrea funesta, which bites big holes in the heads, destroy- 

 ing crowded flower-buds and involucral scales without the least difficulty. To meet 

 this danger a garrison of warlike ants is employed. Honey is secreted from big 

 stomata on the imbricating scales of the still-closed capitula in such quantities that 

 one can see a drop of it on every scale in the early morning, whilst later in the day, 

 as the water evaporates, little masses, or even crystals of sugar are to be found. 

 This sugar, either in its liquid or solid form, is very palatable to the ants, which 

 habitually resort to these capitula during the period of its secretion. And to pre- 

 serve it for themselves they resent any invasion from outside. If one of the afore- 

 mentioned beetles appears they assume a menacing attitude. They hold on to the 

 involucral scales with their last pair of legs and present their fore-legs, abdomen, 

 and powerful jaws to the enemy, as shown in fig. 264. Thus they remain till the 

 beetle withdraws, if necessary hastening its retreat by squirting formic acid in its 

 direction. Then they quietly begin to feed on the honey again. Ants of the same 

 species do not fight amongst themselves on these Composites, although as many as 

 ten to fifteen specimens of the ant Camijjonotus JEthiops live on each capitulum of 

 Jurinea mollis, and about the same number of Formica exsecta on the heads of 

 Serratula lycopifolia. 



As soon as the florets on the heads begin to open, the secretion of honey 

 diminishes and ultimately ceases. No longer do beetles come to devour them, nor 

 is there any further need for protection. The garrison is withdrawn, the ants 

 going away in search of other, younger flower-heads. 



TAKING UP OF POLLEN BY INSECTS. 



Having obtained in the last chapter a general survey of the contrivances in 

 connection with the advent and reception of insects at the portals of flowers, we 

 are now in a position to describe the means whereby insects, after reaching the 

 flowers, are covered with the pollen there awaiting them. 



The simplest case is that where the insects rove and climb about the flowers, 

 and so get powdered all over with pollen. This happens in innumerable Umbelli- 



