from that of zone A. For example, for Acer campestre the constant in zone A for leafing is 0.131, but for zone B it is less than that by 0.039, and would therefore be 0.092.

In the original, from which the foregoing abstract is copied, Linsser gives the so-called probable error or the limit of uncertainty as deduced from the agreement among themselves of the numerous individual determinations of the physiological constants in zone A, whereas the mean values alone are given in our summary. It appears that the uncertainties are larger for the ripening phase than for the leafing and blooming phases, if we consider only their absolute values, but decidedly smaller if we consider their relative. values. In general the uncertainty of the constant for leafing is about one-twentieth of its own value, the uncertainty of the constant for blooming is about one-fortieth of its own value, and the uncertainty of the constant for ripening is about one-fiftieth of its own value.

The values of the constants, as deduced from stations that lie in the dry zone B, vary much more than those in zone A; but this is a necessary consequence of the law of growth, since in such dry regions the quantity of heat required to produce a given phase ceases to be a simple constant and becomes a complex function of the available heat and moisture and depends upon the individual ratio f/w at each station. It will of course be noticed that, with few exceptions, the figures in the columns of departures are negative, thereby indicating that the quantities of heat actually utilized by plants in the dry localities in zone B are less than the quantities utilized by the same plant when it has an abundance of moisture in zone A. Most of the 17 positive figures among these departures relate to the period of leafing, and many of them are but little larger than the limit of uncertainty deduced by Linsser for the respective plants.

All of the plants investigated by Linsser belong, as is seen by the above list of names, to the exogens. They are also perennials, but his intention was to extend this investigation to the herbaceous annuals, and a large mass of work in this direction had been accomplished before his untimely death in 1871.

The conclusions drawn by Linsser from the data, as summarized in his published tables, may be presented as follows:

Although the general fact above mentioned, that plants growing in regions that have scant summer rains utilize less heat and less moisture to produce a given phase of development than similar plants having the same quantity of heat at their disposal with plenty of rain during the summer, might be considered as only a further consequence easily deduced from the principle that underlies the theory of Linsser's physiological constant, yet we may also consider the fact as one established empirically and seek for the most probable explanation. Any general relation between the vital phenomena of plants and their external influences can, according to the ideas established in Linsser's first memoir, be looked upon either as due to temporary influences or as a consequence of the habits of the plant. If we adopt the former view, then the cause of the accelerated development of plants in zone B will consist in the fact that from the beginning of vegetation onward one or more accelerating forces have come into play, the intensity and duration of whose action is greater for stations in zone B than in zone A. Such accelerating forces may consist in a greater quantity of heat or of sunshine or possibly other influBut when we come to examine the temperature curves for stations in the two zones we see at once that heat alone can not be considered as the stimulating force. A similar comparison shows that rainfall during the growing season can not be the stimulus. Again, stations such as Parma and Pessan show that great differences in

ences.