264 A NATURALIST ON THE " CHALLENGER." 



trace of them ; but possibly, if the tissues had been fresher, I 

 should have met with them, for Hoffman has discovered their 

 existence in marsupials. 



Whilst we were hunting along the river bank, numerous 

 bright parroquets were flying about amongst the trees, and a 

 great flock of white cockatoos flew overhead, harshly screaming 

 at the danger. They settled in some trees near, but were far too 

 wary to let me get a shot, though I did my best to creep on 

 them. The smaller bright parroquets are not at all wary as a 

 rule, but are most easily shot. 



Grisebach, in his account of the Vegetation of Australia* 

 dwells on the close relation of interdependence which exists 

 between the tree vegetation and the coating of grass which 

 covers the ground beneath it ; and remarks, that the amount of 

 light allowed by the trees to reach the ground beneath them is 

 rendered more than usually great by the vertical position in which 

 their leaves grow. Hence the growth of the grass beneath is aided. 



It may be that this permitting of the growth of other plants 

 beneath them, and consequent protection of the soil from losing 

 its moisture, besides other advantages to be derived, is the prin- 

 cipal reason why, as is familiarly known, two widely different 

 groups of Australian trees, the Eucalypti and Acacias, have 

 arrived at a vertical instead of a horizontal disposition of their 

 leaves by two different methods. 



The Acacias have accomplished this by suppressing the true 

 horizontal leaves, and flattening the leaf-stalks into vertical 

 pseudo-leaves or "phyllodes." The gum-trees, on the other 

 hand, have simply twisted their leaf-stalks, and have thus ren- 

 dered their true leaves vertical in position. There must exist 

 some material advantage, which these different trees derive in 

 common, from this peculiar arrangement, and the benefit derived 

 from relation to other plants by this means may be greater and 

 more important than that arising from the fact that the vertical 

 leaves have a like relation to the light on both sides, and are 

 provided with stomata on both faces. 



In support of this conclusion I was told, when at Melbourne, 



fc A. Grisebach, "Vegetation der Erde," p. 210. Leipzig, W. Engelman, 

 1872. 



