62 
Notes on Recent Literature. 
growth, a fact which is not always adequately realised. They 
found a smaller loss of substance, or even a small gain, for ever¬ 
greens such as the Conifers, which can begin earlier, by means of 
their old leaves, to make good the loss by respiration. In every 
case the stem, and still more the root, showed a loss due to 
translocation. 
In commenting on the nature and conditions of the awakening 
of activity in spring, the authors suggest that the abundance of 
soil water and stored food lead to a sort of temporary over-feeding, 
with which the large-celled character of the spring wood is 
correlated, and think that the second burst of growth which often 
takes place later in the year (“ Johannistriebe ”) is often con¬ 
ditioned by an abundant water supply; in the latter case also a ring 
of “ spring wood ” is formed. They state, too, that in Scotch firs 
growing on rich lowland moors, where water and food-substances 
are abundant, the wood is almost all of the same character as the 
spring wood. 
They have also investigated the variations in the amount of 
nitrogen and other mineral elements present in the saplings. With 
the single exception of the fir, they find that practically no 
nitrogen was absorbed during the spring while the leaves were 
expanding, and that the time of maximum absorption varied 
according to the species. In the alder, with its root-nodules, 
absorption of nitrogen continued steadily at a high rate from May 
to November. With respect to potassium, calcium, magnesium 
and phosphorus also they find that the time of maximum 
absorption varies for any given element from species to species ; 
while by the same species the various elements are absorbed at 
different times and at rates which vary independently. Thus the 
pine absorbs nitrogen most rapidly in June, calcium in August. 
Such results as these appear to demonsrate the extreme 
importance of the regulation of the mineral supply by selective 
absorption at the roots. They have, moreover, an important 
bearing on forestry, and may help ecologists to explain the 
common association of certain trees in the formation of woods. 
Ramann, in a further paper, has dealt with the mineral content 
of leaves during day and night. With the exception of calcium, 
the various elements show merely fluctuating variations; but 
calcium he found regularly more abundant during the night than 
during the day, whether calculated in terms of total dry weight or 
of the area of leaf-surface. His explanation of this is that 
translocation is more rapid during the day, and that calcium in 
some way or other participates in translocation. It must be 
pointed out that the former is purely an assumption, considering 
the present state of the evidence on the subject of translocation, 
and hence his inference with regard to the role of calcium is pre¬ 
mature and ill-founded. At present we do not even know with 
certainty that translocation occurs at all generally during the day ; 
and before any far-reaching conclusions are drawn as to the 
metabolic significance of any of the mineral elements, it is desirable 
that a closer investigation should be made into the changes in 
mineral content of the blade of the leaf, apart from the midrib and 
leaf-stalk, preferably by the half-leaf method. 
