348 



THE AMilRICAN 



casin Flower, Cypripedium spectabile, should 

 liave been mentioned also. 



But space must forbid further enumeration, 

 though the list of interesting plants might be 

 much extended. As the autumn comes on, too, 

 the Composite plants come out in full force here, 

 including many species of Helianthus, Aster and 

 Golden Rod (SoHdayo), while the rich blue of 

 tlie Fringed Gentian (^Oentiana crinita), and 

 the curious closed Gentian iOentiana Andrewsii) 

 is a sight never to be forgotten, such a perfection 

 of color as can only be rivalled by the intense 

 crimson of our Cardinal Flower {Lobelia car- 

 dinalis), found here along the small river Des 

 Plaines. 



MORPHOLOGY OF LEMNA. 



BY HENRY GILLMAN. 



Some interesting remarks appeared lately iu 

 the Quarterly Jottrnal of Science owthe "Hiber- 

 nation of Duckweed" {Lemn.a). Allusion is 

 made to a series of observations on this point 

 made by M. Van Hoven, and recorded iu the 

 "Bulletin de la Soci6ti6 lioyale de Botaniqiie de 

 Belgique;"' but which I have not seen. As about 

 two years ago I made some observations on this 

 subject, my experience may be worth noting in 

 this connection. It has not been given publicity, 

 though not long afterwards I communicated the 

 facts, in part, to a correspondent who has de- 

 voted much time to the study of the American 

 Lemnacem. It may here be stated that our 

 species of Lemna appear to be identical with 

 those of Belgium. 



Iu the summer of 1868 I placed in my aquarium 

 a quantity of the plants oi Lemna jiolyrrhiza, L., 

 partly with the hope of detecting them blossom. 

 They grew and multiplied till the early winter, 

 when the fronds gradually decayed and disap- 

 peared. Towards spring I noticed at the bottom 

 of the aquarium, adhering to the mud and stones, 

 a number of minute, gem-like bodies, smaller 

 than the head of the smallest pin, and of an in- 

 tense green. These increased in size, and at 

 length assumed somewhat of the appearance of 

 the frond of a small Lemna, finally rising to the 

 surface of the water, where they continued to 

 grow. In the course of a few weeks a large 

 number of these Lemna could be seen iu my 

 aquarium, they having increased by proliferous 

 growth. At this time they presented so closely 

 the characteristics of L. Torreyi, Austin, as to 

 deceive me quite into thinking them that species ; 

 the thin obovate-oblong fronds were of a pale 

 green, but glossy, and barely one-nerved, the 

 root being single. But in the course of several 



days another change took place. The fronds 

 became broader and rounder, lost their glossi- 

 ness, and put on a dull but darker green above, 

 having a faint pink flush beneath. At length, 

 after a further interval, the fronds becoming 

 thick and palmately five to seven-nerved, and 

 changed to a purplish-crimson beneath, the 

 roots being several in a cluster, proclaimed un- 

 mistakably that the plant was Z.poZyrrAiza, L., 

 antl nothing else. 



From the foregoing I am convinced that much 

 of the Lemna which is taken for L. Torreyi, 

 Austin, and L. perpusilla, Torr., and, perhaps, 

 L. minor, L., is no other than L. polyrrhiza, L., 

 in some of its earlier stages. And here arises 

 the question : Is it a more highly developed 

 plant (species) than those others? Oris it de- 

 graded from the condition of L. Torreyi ? I 

 would add that it is somewhat remarkable that 

 this plant (£. polyrrhiza) , though so common 

 in our pools, ponds and rivers, has never been 

 found in blossom in this country. 



According to M. Van Hoven, as given in the 

 Journal, the three species, L. trisulca, minor 

 and arrhiza, preserve their leaves through the 

 winter, remaining on the surface, while only the 

 L. polyrrhiza and gihba produce leaves of a dif- 

 ferent form in winter. He also states that 

 " their roots are exceedingly minute, and at 

 first hidden within the leaf." 



Some weeks ago, when at Eaton Rapids, Mich., 

 a place lately become celebrated through the 

 discovery of those remarkable magnetic mineral 

 springs, I found (June 7, 1870) theiy. minor, L., 

 in blossom— thousands of them in flower. As 

 it is a species which is rarely seen in bloom, the 

 information may be interesting to your readers. 



Late last autumn (18G9) a friend, a well-known 

 botanist from the East, found in the Detroit 

 river a single specimen in flower of the L. tri- 

 sulca, L. It was a gusty day, and as he searched 

 in his pocket for a piece of paper iu which to 

 secure it, the wind suddenly blew it away, so 

 that he could not recover it. But he is too ac- 

 curate an observer for us to imagine that he was 

 mistaken as to its bearing flowers. It is, also, 

 rarely found fertile. 



Though the Lemna generally floats free, its 

 roots suspended in the wafer, and drifted about 

 by every stray breeze or current in the stream 

 or pond, yet I flnd, where the water is shallow 

 enough, it sends its roots into the soft mud at 

 the bottom, thus becoming a fixture. 



1 find the Wolffia Columbiana, Karsten, grow- 

 ing with L. minor, L., in abundance in the 

 neighborhood of Detroit ; but have not collected 

 it in flower. 



