HABITS OF SPECIES OF LEMNZ. 325 
it was 82°. From the run of my series of freshwater tempe- 
ratures, then in progress, it is to be inferred that during the few 
weeks preceding the flowering, the surface must have been 
frequently heated to 80° in the daytime, the nocturnal fall of 
temperature being about half that of the air. Such were the 
thermal conditions under which Lemna gibba flowered. 
Under a lens the gibbous plants had the appearance of pro- 
ducing female flowers, and the separate thin flat fronds male 
flowers, which was due to the circumstance of the pistil alone 
protruding in the one case, and of the stamens, usually two in 
number, alone showing in the other, although in both instances 
the flowers were hermaphrodite. After several visits to the 
ditch, only one or two rare exceptions to this rule were found, 
namely, where the gibbous plants had evolved stamens. It 
seemed, therefore, as if the flowers were functionally unisexual. 
However, no plants in the fruiting-stage came subsequently to 
my notice. Under observation at home, the flat fronds were 
produced by budding by the gibbous plants, the process being 
rapid, and their stamens visible through their substance before 
they floated away. 
The flowering period covered the greater part of July. 
During August the gibbous plants produced abundautly thin 
and flat fronds, which were now flowerless and of a dark green 
hue. These new fronds presented a great contrast in colour to 
that of the mother plants, had in each case a single root, and 
showed the three distinct nerves which, according to Hegelmaier, 
characterize the flatter forms of Lemna gibba. Such proved to 
be the winter plants, and, asin the case of Lemna polyrrhiza, 
they were extensively produced in summer. Their appearance 
in August was accompanied by the death of a large number of 
the gibbous mother plants, both in the ditch and in my vessels 
at home, a result which certainly could not have been the effect 
ot low temperature. The remainder of the gibbous plants pro- 
ceeded actively with the development of winter fronds during 
September and October, and it was not until early in November 
that the characteristic forms of the plant had disappeared. At 
this time their dark green flat offspring were budding freely. 
both in the ditch and at home, some at the surface and some at 
the bottom; but those afloat could always be sunk by a touch; 
and, in fact, it was not until March that the winter plants could 
float independently, though many of them remained at the 
