434 * BOTANICAL GAZETTE [JUNE 
the spring when there is most moisture and when the tempera- 
ture is moderate. Being well provided with food stored within 
their coats they can carry on the processes of vegetation till the 
seedling is well rooted. Thus being more independent of exter- 
nal conditions they have an advantage in establishing them- 
selves in a less favorable environment, such as that of dry sand. 
In considering the vegetation of dune areas, especially those 
of the ‘Michigan sands,” such as appear by White lake, we 
must also bear in mind that some of them are comparatively well 
provided with alkaline earths, that all have some amount of 
these or there would be no tree growth at least. They often 
produce abundant crops of fruit, especially of kinds that do best 
in light soil, like the peach. The prevailing constituent of the 
soil is silex, but microscopic examination and chemical tests 
show that feldspar, mica, pyroxene, and other minerals are pres- 
ent, such as contain potash, soda, lime, and magnesia, the most 
important of the alkaline earths. The pebbles of the shingle 
along the beach are a mixture of various kinds, quartz prevailing, 
but feldspars frequent, with some limestone. This must be the 
case since they are mainly produced by the degradation of drift 
material.. The comminuted sands formed from them must neces- 
sarily contain the same ingredients, though the harder, coarser, 
and more resistant quartz sand will be most conspicuous to the 
eye as well as most abundant. The percentage of ash in the 
wood of such trees as form the principal covering of a dune 
region is relatively small. As seen in the analysis reported in 
the volume of the Tenth Census on the forest trees of North 
America, the pines have an average range of .I9 to .23 per 
cent. The two most common oaks, Q. velutina and Q. coccinea, 
have .28 and .19 per cent. respectively. The white oak and the 
bur oak are higher but are much less common trees. The 
leaves and bark would show a higher percentage, but as they fall 
and the trees decay this is not only restored to the soil but they 
take with them other important ingredients which enter into the 
composition of humus. The beech, sugar maple, basswood, hem- 
lock, and some other forest trees likewise stand considerably 
