Ia a a lt ek ial ale 
ON THE LIFE-HISTORY OF LEMNA MINOR. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
OTIS W. CALDWELL, 
(WITH FIGURES I-59 ) 
THE greatly reduced sporophyte of the Lemnaceze suggests 
the desirability of ascertaining to what extent these reductions 
have affected the gametophyte, and of looking more closely 
into the structures reported for the sporophyte. It is well 
known that flowering lemnas are seldom found, although during 
favorable seasons the vegetative plant is constantly seen in pools 
and slowly moving streams. Therefore, when in August 1897 
an abundance of Lemna minor was found in flower it was decided 
to make an investigation of its morphology, in order to 
supplement previous work on the vegetative structures; to 
determine whether the usual sequences of monocotyledonous 
gametophytes and embryos were present; and to discover any 
suggestions of primitive or reduced conditions. 
HISTORICAL. 
The publications upon Lemnaceze have been numerous, prob- 
ably the most important ~being the monograph by Hegelmaier 
(4) in 1868, in which he gives the taxonomic features and also 
the general morphology in a way which is surprisingly accurate 
when one considers the condition of technique at that time. 
Another publication by Hegelmaier (2) deals entirely with the 
taxonomic features of the group; while in 1871 appeared a more 
detailed description of Spirodela (6) than that in the Monograph. 
Hegelmaier has also discussed the taxonomy of the group, based 
“pon most recent knowledge (12). A similar work has been 
a for the American species by Thompson (16). Barbeck (8) 
1899 
37 
