THE EMBRYO OF LEMNA 
Frederick H. Blodgett 
(Received for publication January 27, 1923) 1 
The writer was fortunate, several years ago, in locating a habitat in which 
Lemnaceae were abundant, with the special feature of regular flower-produc¬ 
tion in L. perpusilla Torr., which is there present. The development of 
normal flowers and mature fruits is the usual thing in this strain, rather than 
the partial development and later degeneration characteristic of L. minor , 
with which Caldwell worked. 2 The stages of development immediately 
following fertilization are in agreement with the description by Caldwell, 
and need not be restated; the following discussion deals with the formation 
of the embryo and germination of the seed, the earlier stages being in agree¬ 
ment with Caldwell’s description in all essentials. 
The Undifferentiated Embryo 
The development of the embryo falls into three stages: ( a ) from the egg 
to the formation of a stem apex or equivalent; (b) development of the 
plumule and cotylar sheath; (c) formation of secondary structures in the 
plumule. 
Reviewing briefly the early stages, the Lemna embryo develops without 
the formation of a proembryo, all the cells formed by the division of the egg 
remaining as part of the final structure. The embryo sac enlarges rapidly 
until it occupies the whole of the nucellus except a small cap of cells at the 
tip (PI. XXVIII, fig. 1); and at the base a neck-like elongation is thrust 
into the chalazal tissues of the ovule. The endosperm cells formed in this 
chalazal neck quickly become dense in content, but the endosperm in other 
parts is less well developed, showing large cells with weakly staining con¬ 
sents during most of the period of development of the embryo. No sus- 
pensor is formed, the cells which first develop in contact with the inner sur¬ 
face of the embryo sac persisting throughout later stages, and not degenerat¬ 
ing as do the cells of a suspensor when present. A secondary effect of 
fertilization in Lemna is the formation, from the tissues of the integuments 
immediately about the micropyle, of a structure best designated as an 
“operculum.” This consists of cells greatly enlarged and with thicker 
walls than the rest of the integument, and at germination is thrust off as a 
cap by the elongation of the hypocotyl. As shown in figures 1, 2, 3, and 5, 
1 Published, at the expense of the author, out of the order determined by the date of 
receipt of the manuscript. 
2 Caldwell, O. W. Life history of Lemna minor. Bot. Gaz. 27: 37-66. 1899. 
336 
