276 Transactions. — Botany. 



however, are for the most part nearly extinct, so this method 

 of distribution no longer exists. However, as Mr. G. M. 

 Thomson points out for New Zealand, introduced birds (50, 

 p. 317) are now playing a most important role in the spread 

 of plants ; indeed, they may very well supply the place of 

 the indigenous birds in this particular. Myrsine coxii is 

 the first of all the Chatham Island trees to come into bloom, 

 flowering as it does from the end of July. 



Most of the swamp formation of Chatham Island has been 

 much modified through consolidation of the soil consequent on 

 the trampling of cattle and horses, which also destroy the 

 trees which otherwise would seize on the "reclaimed" ground; 

 so instead of following its natural course and becoming a forest 

 the swamp becomes gradually transformed into meadow land, 

 in which certain native and introduced plants which are not 

 destroyed by the grazing of animals become dominant and 

 form a turf. 



Lowland Forest. 



The climate of Chatham Island is distinctly a " forest cli- 

 mate" (48, p. 178) — that is, the whole island would be covered 

 with forest were the edaphic conditions suitable. These con- 

 ditions vary much for different kinds of trees, but, generally 

 speaking, the soil must be deep enough for the trees to become 

 firmly fixed ; it must be firm, but loose enough to contain a 

 sufficiency of oxygen ; it must be well watered, but not satu- 

 rated with water ; and there must be enough drainage to for- 

 bid stagnation. In addition, humus is usually present in large 

 quantities, while nitrifying bacteria and various fungi abound. 

 Finally, there must not be too great a quantity of inorganic 

 salts or of humic acids in the soil (53, p. 292). From the 

 above it is easy to see the reason why, notwithstanding its 

 forest climate, so much of Chatham Island is without trees, 

 since so large an area is occupied by swamps, bogs, and wet 

 ground. It is not quite so easy to understand how a large 

 area quite suitable for tree-life is also treeless, being occupied 

 chiefly by the fern Pteris esculenta. In the section of this 

 paper dealing with burning of the vegetation an explanation 

 of this anomaly is suggested. 



The lowland forest of Chatham Island, though consisting 

 of trees very much smaller in their dimensions than those 

 which make up the forests of New Zealand, are distinctly 

 forests nevertheless, and not mere assemblages of large shrubs. 

 Below, all the trees have bare trunks, sometimes of consider- 

 able thickness, and above, spreading branches covered with 

 abundant foliage. Seen from a distance the forest is blackish- 

 green in colour, but not nearly of so dark a hue as is the sub- 

 alpine Fagus forest of New Zealand. If a forest be viewed 



