1882.] 
411 
[Trelease. 
sues or tissue systems. Non-sexual multiplication is effected by a 
process of budding which gives rise to plants similar to the parent ; 
and as these plantlets bud in their turn, and offspring and parents 
frequently remain attached for several generations, irregular colo- 
nies of loosely connected individuals are commonly found, PL 6, 
figs. 1-3. Sustained by the air in the large intercellular cavities, the 
single plants or colonies fioat upon the surface of the pools in which 
they occur ; and so rapid and effective is the process of budding that 
bodies* of water which in spring contained very little Lemna may 
be covered by a dense film of these minute plants by the middle 
of summer. 
Contrasted with the abundance of the budding individuals, is 
the relative scarcity of flowering specimens. In many localities 
they are never found, although myriads of sterile plants may be 
seem On the other hand, where flowers have once been found 
they may be confidently looked for at the proper time in succeed- 
ing years ; and as a general thing where found at all they occur 
in great abundance. The local influences which oppose or favor 
sexual reproduction are, so far as I am a\yare, unknown. 
Each fertile frond produces a single flower from a fissure in its 
side quite similar to that from which new plants are commonly 
formed by budding, figs. 1-3. A pistil, two stamens, and a sub- 
tending bract or spathe constitute the entire flower, fig. 4. 
When it expands, if such a term be allowable when speaking of so 
simple a flower, the pistil elongates sufficiently to expose about 
half its length beyond the lips of the marginal fissure of the frond, 
in which it had been concealed, fig. 1. The stigma, a depression 
in the tip of the style, becomes moist by the exudation of a fluid, 
and is now receptive, as shown by the prompt development of tubes 
from pollen grains placed upon it. In this practically unisexual 
condition the flower remains some days ; then a stamen — that fur- 
thest from the base of the frond — becomes exserted, and, having 
reached a length somewhat greater than that of the pistil, becomes 
dehiscent, its pollen remaining heaped in the open cells of the 
anther, fig. 2. Several days later the second stamen appears at the 
edge of the frond, elongates until it is about equal to the pistil, and 
in its turn dehisces, fig. 3. 
The variability that has frequently been noticed in the duration 
