1899 ] LIFE-HISTORY OF LEMNA MINOR 63 
are not abundant, and the bud is more nearly spherical. It must 
be borne in mind, however, that winter buds are formed only 
when the environment is becoming unfavorable. For this reason 
fewer air spaces are developed, and the cells do not divide so as 
to increase the bud in length. The greater rotundity of the 
winter bud, therefore, is not due to increase in thickness, but 
rather to decreased length, as compared with the ordinary sum- 
mer buds. Since few air spaces are developed and gases are no 
longer actively produced, when the bud becomes free it sinks to 
the bottom of the pond or stream, or remains suspended in the 
water a little above the bottom. When the conditions again 
become favorable the bud begins to grow while in the winter 
position, and soon produces sufficient air spaces and gases to 
cause it to come to the surface of the water. By this time it 
has usually begun one or two new vegetative fronds. 
My observations do not indicate that winter buds necessarily 
follow the production of flowers as stated by Guppy (10). A 
large number of cases were observed in which the usual summer 
frond develops at the same time that the flower is formed, or 
immediately afterwards. Hegelmaier doubts whether winter 
buds are ever formed in the tropics. 
Flowers.—The ecological significance of the conditions of the 
flower of Lemna minor is very suggestive. It is known that 
flowers are developed very infrequently, and when one considers 
that in most of those formed the embryo sac structures and 
ovules break down at various stages in their development, result- 
ing in great paucity of seeds, it becomes evident that the condi- 
tions which favor vegetative multiplication have led to great 
reduction of ordinary seed formation. The device of winter buds 
also greatly assists the plant in discontinuing the seed habit. 
SUMMARY. 
1. The sporophyte of Lemna minor cannot be definitely 
homologized with either a stem or a leaf, but is a shoot undiffer- 
entiated except at the basal and nodal regions. 
2. The secondary root is formed froma group of hypodermal 
