CL 



s 



THE IMPORTANCE OF HAIRS IN PLANT LIFE 79 



than one hundred small flies will be found, and mentions, on the 

 authority of Knuth, an instance of 4000 being found in a single 

 Arum. It is possible that the honey is exactly the food this species 

 of fly (Psychoda) loves best, or the smell may prove an over- 

 powering attraction. Other very opposite explanations have 

 been given lately. Father Gerard's opinion, quoted by Lord 

 Avebury, is that the honey has a stupefying effect on the insects, 

 which he says are killed and digested in the chamber, for the 

 dried remains of flies are found on the walls of the cavity. It is 

 quite probable, however, if flies visit the flower in such numbers, 

 that some should get killed, owing to the want of oxygen ; the 

 presence of a large number alive is a fact 

 largely in favour of the usually received 

 theory. 



Hairs may entangle the desired insects, 

 but they may also keep away undesirable 

 guests, thus guarding the nectary and pre- 

 serving the honey for the insect able to 

 pollinate the plant. In the Dead-nettle 

 the honey is secreted by a nectary just 

 below the ovary, and it collects at the 

 bottom of the corolla. Here there is a ring 

 of hairs which effectually prevent small FIG. 45. Median vertical 

 insects getting the honey, for the Humble- 

 bee is the species best adapted to the 

 structure of the flower. 



Sometimes flowers have no honey, and 



insects visit them in order to get pollen with which to feed their 

 young. Under these circumstances some flowers have special 

 staminal hairs to which the insect clings. The mulleins are 

 good examples of this. The Black Mullein, in particular, has 

 on its stamens a row of rich violet-coloured hairs. In all these 

 ways hairs are of use in pollination. 



DISPERSION OF FRUITS AND SEEDS. Many fruits are dispersed 

 by hairs or bristles. It is well known that in many of the Com- 

 positae the sepals are represented by hairs. After the formation 

 of the fruit those develop into organs of dispersion. The 



section of flower of 

 Dead-nettle, a, an- 

 thers ; s, stigma ; h, 

 hairs. 



