230 PROCEEDINGS OF THE ACADEMY OF [1880. 



ON THE DEVELOPMENT OF LEMNA MINOR. 

 BY WM. BARBECK. 



In the early part of last April, I found, in a little pond near 

 Gamden, N. J., among patches of Riccia fiuitans^ a number of 

 minute brownish bodies, which under the lens had very much the 

 appearance of germinating spores, showing at the top a greenish, 

 prothallium-like outgrowth. They were of an oval form, and less 

 than a millimetre in size. 



I secured several of these little bodies, and, upon further exam- 

 ination under the microscope, I found that the}' contained a well, 

 developed embryo, which was enclosed by a comparatively large 

 cotyledon. Thus they were evidently the seeds of some mono- 

 cotyledonous plant. 



I was not able to return to the pond until a week later. Within 

 this week the germination had been completed in a number of 

 specimens, and numerous little plants were developed, most of 

 them still in connection with the seed. These obovate, indis- 

 tinctly three-nerved individuals, with a single root hanging from 

 the under surface, were apparently Lemna minor. Thousands of 

 fresh seeds had meanwhile appeared at the surface of the water, 

 most of them germinating, and thus I could get the specimens in 

 all stages of their development. I have tried to show this gradual 

 development (up to the completion of the second frond) by a 

 series of illustrations, Plate XVIII. 



Figures I and II represent longitudinal sections through a seed 

 in which the germination is about to commence. (Fig. I is from 

 the centre, Fig. II from a part nearer to the surface). 



The seeds are seen surrounded by a comparatively strong 

 coat, the testa (^), which is considerably thickened towards the 

 top, where it covers the lid, or operculum (o), by means of which 

 the mycropyle is closed. In [c) we have the large cotyledon, 

 surrounded by a scanty layer of endospermium (sp.) ; in (u) and 

 (wj) the two lobes into which the cotyledon will afterwards split, 

 begin to be differentiated. The axis of the embryo (e) forms an 

 obtuse angle with the medial line of the cot3dedon. In {p) we 

 have the plumula, in {r) the radula of the embryo ; (/) indicates 

 a fissure inside of which the gemma of the second frond is being 

 formed. 



