2 40 THE PHYSIOLOGY OF PLANTS 



from a short-styled form.^ We might add to these instances 

 of heterostyly a description of other mechanisms of flowers 

 which render it necessary for a plant to have special carriers 

 or distributors of pollen (fertilising agents). We need only 

 refer to the compact pollen masses (pollinia) of the Orchids, 

 which could never reach the stigma of their own accord, and 

 to the monoecious and dioecious plants. In the case of the 

 latter, e.g., the Conifers, Willows, Poplars, Oaks, &c., the wind 

 will transport the pollen from flower to flower. Such flowers 

 are therefore termed anemophilous, in contradistinction to those 

 in which insects involuntarily, no doubt, perform the pol- 

 lination (entomophilous). This is the case in the Orchi- 

 dacese, AristolochiaB, and many Papilionacese and Labiatae. In 

 some few water-plants (Vallis7ieria, Ceratophyllum) the water 

 carries the pollen from one flower to the stigma of another 

 one (hydrophilous). 



Especially in the case of entomophilous flowers do we find 

 the most curious mechanisms for the employment of insects 

 for the purpose of pollination ; but we must content ourselves 

 with a single instance. 



In the year 1885, the Society for Acclimatising introduced 

 into its gardens in Canterbury, New Zealand, the first humble- 

 bees. In the next year these insects had considerably increased 

 in numbers, and it was then found that the common red clover, 

 which had been introduced into that country, but had formerly 

 only produced very few seeds, now yielded very good seed- 

 crops. The humble-bees, which in this country fertilise the 

 flowers, had till then been missing. 



Bees and humble-bees play a very important part in the 

 fertilisation of flowers, carrying the pollen from flower to 

 flower by means of their hairy bodies. They sometimes, how- 

 ever, bore holes into flowers, and then obtain the nectar or 

 honey without pollinating the flower. This is the case in the 



1 The pollination of heteromorphic forms with pollen from a similar form 

 of flower has been designated by Darwin an "illegitimate union." The 

 legitimate union consists of the pollination of flowers with pollen from a dis- 

 similar form. Such a beneficial result of cross-fertilisation has not been uni- 

 versally proved — indeed, in some cases self-fertilisation results in a plentiful 

 crop of seeds ; yet gardeners will do well in all cases to transfer pollen of one 

 flower on to the stigma of another flower. 



