1887-88.] Heterophylly in New Zealand Veronicas. 245 



off bodily, leaving a well-marked scar, resembling- some 

 conifers in this respect as well as in general appearance. 



It may reasonably be conjectured that the remote ances- 

 tors of the Veronicas mentioned originally had leaves of one 

 form only, resembling more closely than they at present do 

 the ordinary species of the genus, and that, through change 

 of environment or some such cause, these leaves have become 

 altered as we now find them. The heterophyllous condition 

 might thus be explained as being a tendency to revert to the 

 original type. 



Observations on the Annual Increase in Girth of Trees in the 

 Royal Botanic Garden, and at Craigiehall, near Edinhiirgh, 

 from 1878 to 1887. Part I. By Dr Christison, Edin- 

 burgh. 



(Read 12tli July 1888.) 



In March 1883 I communicated to the Eoyal Society of 

 Edinburgh the results of five years' observations on the 

 increase in girth of trees, begun in 1878 by Sir Eobert 

 Ohristison, and completed by myself in 1882. The same 

 trees having been under observation for five additional years, 

 I now present the results for the whole decennial period, 

 1878-87. In the later years of that period monthly as well 

 as annual observations were taken; but, as the former were 

 fully discussed in a paper read to this Society last summer, 

 the present investigation is confined entirely to the annual 

 observations. 



In estimating the value of the results, two disturbing 

 elements have frequently to be taken into account. One is, 

 that a considerable number of the trees seem to have been 

 selected at too great an age for the purposes in view; not 

 that they were actually of great age, but because the thin 

 sandy soil of the Botanic Garden seems incapable of support- 

 ing tree life in full vigour after a moderate age, in most 

 cases. The other disturbing element is the occurrence, early 

 in the decennial period, of three successive seasons of almost 

 unprecedented severity, which left their impress on the girth 

 increase, not only at the time, but in some species to the 

 very end of the period, if not permanently. The general 



TRANS. BOT. SOC. VOL. XVII. JB 



