TREES OF THE CAMBRIDGE BOTANIC GARDEN. 19 



case of Quercus obtusaia. Here is a Mexican Oak so like the common 

 pedunculate Oak that a diagnosis of the one is almost the same as the 

 diagnosis of the other, the contrast being hardly more than a slight 

 difference in the length of petiole, a difference that might easily occur 

 in the same species. In the case of the Mexican Oak; however, the 

 leaves may remain on the tree until March, and it was pointed out 

 also that leaves may suffer from cold winds early in December or 

 remain uninjured with slight protection, features that are evidence 

 of a constitution quite unlike that of the pedunculate oak. Another 

 instance was given in the case of Tilia fietiolaris, regarded byELWES 

 and Henry as a variety of T. iomentosa (T. alba) ; other botanists, 

 however; believe that this tree is distinct as a species. Ordinary 

 evidence to this effect is found in the greater length of petiole, but 

 it is supported by the fact that the flowers are poisonous to bees, an 

 indication of some essential difference, though it may be admitted 

 that, according to report, plants may vary in being toxic or not, e.g. 

 Solarium nigrum. A third instance was mentioned in the case of the 

 Lombardy Poplar. It is usually regarded as a fastigiate form of 

 Populus nigra. Dr. Moss, of the Cambridge Herbarium, however, 

 remarks that the differences are numerous, and he, as well as other 

 botanists, believes that it must occur in a wild state. Here it may be 

 pointed out that the shape of the tree is very unusual for a wild one — 

 in nature the leaf -system of a tree is not subjected to the disadvantage 

 of this habit of growth — and the lecturer suggests that, while probably 

 not a fastigiate form of the common Black Poplar, it is a fastigiate 

 form of an ally not yet recognized, and is therefore not entitled 

 to specific rank as Populus italica. 



An interesting point forced itself upon the attention when 

 taking the measurements of trees at intervals of three or four 

 years, though it is in fact nothing more than might be expected. 

 This point is with regard to the altering relation of diameter to 

 height as growth proceeds and age increases. It appears that under 

 certain given conditions a tree may cease to gain much in height — 

 while under other conditions capable of growing much taller — and 

 instead gain much in spread of branches. There are several instances 

 in the Cambridge Botanic Garden, and this seems to show that it is 

 not a case of individual peculiarity, but one instance may suffice — 

 that of Paulownia iomentosa', of which there is a healthy and free- 

 flowering tree in the Cambridge Garden. In the Paris Botanic Garden 

 there is a tree that was 60 feet high in 1904, and at Westonbirt, Glou- 

 cestershire, a tree that was 56 feet high in 191 1. At Cambridge a tree 

 that is now 23 feet 4 inches high has gained only the odd 4 inches in 

 four years while increasing in diameter from 27 feet to 28 J feet in the 

 same time. Other, even more striking, instances could be given. 



The lecturer desired to ask that observations should be made by 

 those who have the opportunity with regard to the power that trees 

 seem to have of altering the direction of large branches for the 

 purpose of disposition to the best advantage. All the lower branches 



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