TRANSACTIONS OF SECTION K. 673 
5. Some Observations on Spireea Ulmaria. 
By Professor R. H. Yapp, M.A. 
In a previous communication * the author described the curious seasonal 
differences, in respect to hairiness, which are to be found in the leaves of 
Spirea Ulmaria. It was then shown that the leaves unfolded in the spring- 
time are successively glabrous, partly hairy, and finally densely hairy. 
Further observations have shown that in the case of rhizomes, which do 
not develop into erect flowering shoots, this increasing hairiness is only 
found up to about the middle of July. The leaves unfolded subsequently 
to this exhibit decreasing hairiness until autumn, when glabrous leaves are 
again formed. 
The author showed that the production, in nature, of glabrous or hairy 
leaves coincides in a remarkable way with the changes in (1) the evaporating 
power of the air and (2) light intensity. This is true whether the vertical 
changes in these factors (due to the density of the vegetation) or the annual 
march of evaporation and light intensity are considered. 
It is difficult to influence the hairiness of Spirea leaves merely by 
altering the external conditions. But the hairiness is very distinctly 
reduced by growing the plant in deep shade, if at the same time the 
atmosphere is constantly kept humid. 
6. The Delayed Germination of Seeds. By Professor L. H. PamMEt. 
In 1901 the author began a study of the germination of weed seeds kept 
under different conditions. It was soon discovered that a large number of 
weed seeds failed to germinate in the fall as they should, and a more 
extended work was begun in 1902, keeping some of the weed seeds in paper 
packages, while others were stratified in sand and subjected to the environ- 
mental conditions of an Iowa winter. Mr. H. 8S. Fawcett, under my direc- 
tion, made a study of a large number of weed seeds. He found on germinat- 
ing seeds each month from November until May, and another sample in 
May which had been exposed to the weather, that the general effect of the 
freezing and thawing was to increase the percentage of germination, espe- 
cially of seeds with hard coats; stratification lessened also the dormant 
period in the case of wild rye from nine to five days; the common fox-tail 
(Setaria glauca) from eleven to seven and a quarter days, while the per- 
centage germination of this plant was increased from 34% to 38 per cent. 
Subsequently the author and Miss Charlotte M. King made a study of 
the germination of seeds of 130 species of weeds. As in the previous ex- 
periment, seeds were placed in paper packages and planted each month. 
Another lot was stratified in sand and subjected to an Iowa winter. The 
experiment was started in the fall of 1905, continuing until April 1909. 
The germination of the seeds was remarkably low during all the months, 
but in most instances the germination was better in samples stratified in 
sand than those kept in paper packages. Many of the seeds germinated in 
a very irregular manner, better in some years than others. It is evident 
that the factors influencing the germination of many of our weed seeds and 
species of plants are not known. A study was also made of old clover seed. 
It was found that the scratching of clover seed and treatment with sulphuric 
acid in some cases hastened the process of germination, but not in all. 
Finally, it was found with reference to the soft maple (Acer sac- 
charinum) that this seed soon loses its vitality, but that it may be kept for 
weeks in a refrigerator without materially losing its vitality. The thin 
seed-coats cause a rapid loss of water from the cotyledons, and hence 
1 Brit. Assoc. Rep., Leicester Meeting, 1907, p. 691. 
1909, xX 
