Thomson. — Botanical Evidence against Recent Glnctation of N .Z . 353 



I have made a series of experiments to test the amount of transpiration 

 undergone by different plants, and these show interesting results as far as 

 they have gone ; but as only a limited number of plants have been ex- 

 amined up to the present, and the whole series seems to be worth conc-luding, 

 I will not give more than a single example to illustrate the facts. 



The method adopted was to take a newly cut leafy twig of Fuchsia 

 excorticata (as a control), weigh it, and hang it up in a dry place for a stated 

 time. Twigs or branches of the other plants to be tested were treated 

 in the same way and for the same period of time. The method is not a 

 very accurate one as a test of transpiration, but it gives comparative results 

 which are suggestive. It only shows the actual loss by evaporation, but 

 gives no correct idea of the amount of water which the plants tested 

 could abstract from a constant water-supply and give out to the atmo- 

 sphere through their breathing-surfaces. Still, the following facts are 

 interesting : — 



In Fuchsia excorticata there are no stomata on the upper surface of the 

 leaves, but as many as 228 per square millimetre on the underside. These 

 are all placed on a nearly level surface, so that when much evaporation 

 takes place the whole leaf tends to wilt and wither. 



In Veronica Hectori (a xeroph^-tic form) there are also no stomata on 

 the upper or appressed side of the leaf, but on the lower (outer) side there 

 are about 128 stomata per square millimetre. These are placed in some- 

 what deep pits, so that when much evaporation takes place the guard cells 

 above them overarch and tend to close the orifice, and the leaves show no 

 sign of wilting. 



A small leafy branch of Fuchsia excorticata exposed to dry air for twenty- 

 eight hours lost 6641 per cent, of its weight ; a branch of Veronica Hectori 

 exposed for the same time to the same conditions lost only 8-33 pe • cent, 

 of its weight. This illustration is typical of the whole series : some lose 

 a greater and some a lesser proportion of their moisture ; but in all these 

 220 species of plants the amount lost by transpiration is very small when 

 compared with a thin-leaved plant like the Fuchsia. 



The cause which has led to the development of this desert flora would 

 appear to be the extremely dry conditions which prevail on the eastern 

 side of the main range of the Alps. Thi? is brought about by the moisture- 

 laden winds which strike the range from the north-west losing their water 

 as they are forced over the momitain barrier, and descend on the east side 

 as dry, hot winds. The average rainfall along the western side of the 

 Southern Alps probably everywhere exceeds 100 in. ; on the eastern side 

 it is in many districts less than 20 in. It is impossible to get exact records, 

 for they have not been kept ; but on the Ida Valley Station, in Central 

 Otago, where rain-gauge records were kept for a few years, I am informed 

 the rainfall was always under 15 in. per annum, and in some seasons fell 

 as low as 10 in. This extreme dryness, coupled with the intense winter 

 frosts, has caused the disappearance of nearly all plants except such as were 

 able to withstand these severe conditions. The average height of the main 

 range may be taken as 7,000 ft. : if the range were elevated another 5,000 ft. 

 it would produce a still more severely desiccated region, in which only a 

 xerophytic flora could survive, and it would also account for all the Otago 

 lakes and West Coast Sounds, and all the glacial phenomena required to 

 explain Professor Park's views. Only it was probably much further back 

 than the Pleistocene. 

 12— Trans. 



