June, 1923 ] 
BLODGETT — EMBRYO OF LEMNA 
341 
Flowering Plants 
In the strain under discussion, the tendency of the plants to produce 
flowers is so strong that flowers have been found upon specimens still retain¬ 
ing the adherent seed coats and the clasping sheath of the cotyledon. These 
flowers had come as the second generation of outgrowths from the plumule, 
or as the equivalent to L 3 in frond sequence. It is to be noted that in these 
cases, as in more mature specimens, the flowers are produced from the 
pouch in the reentrant angle formed by the fronds, rather than projecting 
from the outer and protruding angle at their junction. This would preclude 
any possibility of floating contact between plants as a means of pollen 
transfer, as two flowers would be separated by the combined distance of 
their respective angles, which distance approximates the length of the frond 
itself. The stigma is elevated above the surface in such a manner as to 
avoid contact with the surface so far as possible, so that floating pollen is 
not a likely means of transfer from stamen to pistil. Further, the pollen 
grains are spinose, as in many insect-carried forms, which fact would 
indicate the possibility of insect assistance here also. In the habitat con¬ 
cerned, there are a number of species of Thysanura, and other minute 
insects in considerable abundance. The actual assistance of these in the 
pollination of Lemna has not as yet been proven, but their presence among 
the plants, and the spinose character of the pollen, are at least suggestive 
of insect aid, and may explain the regularity of seed-formation in this 
locality. This point is still under investigation as opportunity offers, but 
it was not thought wise to defer indefinitely the publication of other results 
in respect to the sporophyte of Lemna perpusilla. 
Summary 
The embryo of Lemna develops without the formation of suspensor 
cells or proembryo; all the cells formed from the egg evidently going to 
the formation of the true embryo. No radicle is formed, even in rudiment, 
by this species, and the cotyledon is terminal and massive. 
The stem apex appears as a lateral mound of cells about midlength of 
the embryo when 12-15 cells in length, and develops directly into the first 
leaf, or plumule. 
The plumule elongates at the same time that it is being enclosed by an 
overgrowth backward from the base of the cotyledon, and is turned into a 
position parallel to the hypocotyl. 
When fully developed, the plumule is obliquely cordate at base, flattened 
lens-shaped, and completely enclosed by the cotylar sheath; the tip of the 
plumule and the apex of the enclosing sheath lie just under the micropyle. 
A daughter frond is early formed in the larger basal lobe of the plumule, 
and this develops the first root structure formed in this species. 
>In basal pouches of the daughter frond, paired frond rudiments are 
