THE AMERICAN BOTANIST 107 



almost continuously, and when such plants are moved into 

 temperate regions frost finds them without well developed 

 terminal buds, but in our forest trees, the twigs grow to a 

 certain length and then the plant rests whether cold has come 

 or not. The elm, however, is in a different category. Early in 

 the year it completes its spring growth, but along about August 

 it suddenly starts up anew and within a few weeks lengthens 

 its branches several inches more. The bright yellow-green of 

 the new leaves forms a striking color contrast with the foliage 

 produced earlier in the year. A number of other trees have 

 the habit of producing a second growth late in the season, but 

 there are few in which it is as noticeable as it is in the elm. 

 The cause of this resumption of growth is generally thought 

 to be connected with the amount of moisture in the soil, but 

 the elm appears not to be so influenced, for it produces its new 

 growth just as readily in the midst of a drouth as during more 

 propitious seasons. 



Distribution of the Oaks. — The genus Quercus, to 

 which the oaks belong, is far more widespread and contains 

 more species than those who have seen only their native species 

 are likely to have imagined. We commonly assume that the 

 oaks are a typically northern genus, but many species are 

 found in the tropics. The genus seems to be especially well 

 represented in Japan, Formosa, China, Burma, Java, Sumatra, 

 Borneo, the Philippines and other tropical islands. South 

 America and Africa, however, have no oaks. A writer in a 

 recent number of the Japanese Botanical Magazine lists nearly 

 450 species of oaks. About half of these, formerly placed in 

 the genus Quercus are now to be found in the genus or sub- 

 genus Synadrys. Many of the species in this latter group have 

 the nuts entirely surrounded by the involucre or cup, in this 

 suggesting their relation to the walnuts and hickories, A large 

 number of the tropical species have entire leaves and of course, 

 are evergreen. 



