xxxm SEED-DISPERSAL AND GEOLOGICAL TIME 509 



I should be inclined to think that the tropical genera of the 

 New Zealand flora, more especially of the forest flora, reached that 

 region during the glaciation of the northern hemisphere, when 

 the Indo-Malayan plants were, so-to-speak, cornered in the 

 Western Pacific. Yet it must be noted that these are, as a rule, 

 genera that either display an indifference to the varying thermal 

 conditions of different latitudes or are known to at times extend 

 their range beyond the tropics. Thus Elaeocarpus and Freycinetia 

 are equally at home in the temperate rain-forests of New Zealand 

 and in the tropical rain-forests of Polynesia and Malaya ; whilst 

 widely-spread tropical genera like Pittosporum and Peperomia, 

 that occur in New Zealand, exhibit their power of adaptation to 

 varying climates by extending outside the tropics in other regions 

 and by their vertical range in the Hawaiian mountains, where they 

 are found alike at low elevations a few hundred feet above the sea 

 and at altitudes of 6,ooo or 7,000 feet. 



All these plants, however, are in a relative sense recent 

 intruders. When the student of dispersal looks at the long list of 

 the conifers of the New Zealand forest flora and reflects that he 

 knows but little of their means of dispersal, and that if his 

 acquaintance were far greater it would not avail him much, he has 

 no choice but to take his place behind the earlier investigators of 

 the flora, and to see in these trees evidence in favour of a remote 

 continental period, probably referable to the mesozoic age. 



A Discussion of some Means of Dispersal. — Not many authors 

 seem to have discussed the possibility of insects as agents of seed- 

 dispersal in the Pacific. They appear to me quite suited for 

 transporting the spores of ferns and lycopods as well as the minute 

 seeds of plants like the orchids and the begonias. Darwin, who 

 allowed few possible means of dispersal to escape his notice, pro- 

 cured the germination, as my readers will remember, of grass seeds 

 found in the dung of Natal locusts. When on the barren summit 

 of Mauna Loa, I noticed that the recently dead bodies of some 

 butterflies, that had been carried up the slopes from the forests 

 below by the "southerly updraught," were already attacked by 

 bugs, parasites that must have been transported from the Lower 

 regions by some of the numerous larger insects that are blown up 

 the slopes. 



In Note 61 the occurrence of the wind-blown insects on the 

 summit of Mauna Loa is described. That insects can be 

 transported into the upper regions of the atmosphere by ascending 

 air-currents was long ago remarked by Humboldt, and the subject 



