325 



(The number of slight diseases in obtainable by subtracting the 

 4 severe ' from the ' total ' in the respective cases. The total number 

 of insects listed was 385). 



Columns 6 and 8 are worthy of special comparison. 



" Of the insects mentioned here as attacking young trees, 102 spe- 

 cies attack the Conifers only, 18 attack the Conifers and dicotyle- 

 dons, and 15 species attack the dicotyledons only. Thus, on the 

 average, each Conifer has 25.5 exclusive foes or 30 inclusive foes, 

 while each dicotyledon has 2.5 exclusive foes or 5.5 inclusive foes. 

 Similarly, attacking old trees, 121 are confined to the Conifers, 

 8 damage the Conifers and dicotyledons, while 131 are confined 

 to the dicotyledons. On the average each conifer is attacked by 

 30.25 exclusive foes or 32.25 inclusive foes, and each dicotyledon 

 by 21.8 exclusive or 23.1 inclusive foes. 



" Thus dicotylous trees (at least in north ( temper ate climes) may 

 owe their victory over Coniferae in the majority of favourable sites 

 largely to their power of resisting or repairing injury caused by 

 sudden hostile influences, including animal and fungal foes. It is 

 possible, too, that in secular changes of climate Coniferae suffered 

 more than dicotyledons, though certain coniferous genera, such as 

 Pinus, betray no signs of inability to secular acclimatization. So 

 far as the chief forest trees are concerned, insect-pollination appears 

 to have played but a small part in aiding the north-temperate di- 

 cotyledons." 



The following is the Summary of Mr Groom's paper: 



1. The northern evergreen Coniferae are architectural xero- 

 phytes in which the extensive surface exposed by the evergreen 

 leaves as a whole renders it necessary for the individual leaves to 

 be xeromorphic in form and xerophytic in structure. This type of 

 structure enables these Coniferae to live in regions where there is 

 a season of physiological drought, in situations varying from dry 

 dunes to moist forests, and from arctic and alpine situations to tro- 

 pical sites. 



2. The tracheidal structure of the wood of these conifers is 

 well suited to their xerophytic evergreen leaves ; and a similar type 

 of wood is apt to occur in north-temperate and austral-temperate 

 dicotyledons that have evergreen xerophytic leaves, as is shown by 

 American species of Quercus, Trochodendron, and Drimys. The 

 tracheidal structure of the wood is not a bar to progress and to 

 the adoption of the deciduous habit, for in the larch a rapid trans- 



