88 



held fast by the sticky secretion, and the tentacle bends over 

 and deposits it on the centre of the leaf. But this stimu- 

 lates the short central tentacles, and so all the other large 

 tentacles bend over and enclose the victim. When the prey 

 is thus secured, the glands proceed to secrete a ferment that 

 digests the insect, and the products are absorbed by the leaf. 1 



In Scorpiurus the pod containing the seeds in some 

 species closely resembles a caterpillar, with the result that 

 insectivorous birds are tempted to seize it. They probably 

 carry it some distance before discovering the mistake, and 

 thus distribute the seeds. 



In Acanthorhiza adventitious roots provide a thorny 

 palisade above the ground at some distance from the tree, 

 thus preventing the approach of animals. 



There are also remarkable co-adaptations between plants 

 and animals, particularly in relation to the pollination of 

 the former. In flowers that depend upon insect pollination 

 we have every gradation from forms where the honey, which 

 serves to attract insects, is freely exposed, to those where 

 the honey is so protected that only insects with very long 

 tongues can reach it. It is impossible to deal with many 

 examples here, but the co-adaptation between the Yucca 

 and a moth (Pronuba) is particularly striking. The Yucca 

 has a large white flower, which emits a strong perfume, 

 particularly at night when it is visited by the moths. The 

 female at first collects the pollen. This she rolls into a 

 pellet, using for this purpose maxillary appendages specially 

 modified and found only in this genus. She continues 

 doing this until she has made a pellet about three times 

 as large as her head. She then proceeds to lay her eggs 

 inside the ovary of another flower. She does this by means 

 of an ovipositor, which is sufficiently sharp to penetrate the 

 tissues of the ovary and sufficiently long to reach the inside. 2 



1 Darwin, Insectivorous Plants; Pf'efFer, Unters. lot. Inst. Tubingen, i. 

 483, 1883 ; Rosenberg, Phys.-Cytolog. Unters. iiber Drosera rotundifolia, Upsala, 

 1899. 



2 The possession of a long and sharp ovipositor by a moth is very remarkable. 



