68 BOTANICAL GAZETTE. 



Woljfia and Lemna by the coherence for a time of the proliferous 

 parent to its offspring. The yielding to currents of water is a mat- 

 ter of indifference, unless it be to carry the plant into new food 

 regions, which is certainly not well accomplished in some ponds. 

 The disconnection with "the soil keeps the stomata above water 

 in the ever changing level of ponds. This is a matter of prime im- 

 portance to leaves of the second class. A root that would bind our 

 Wolffia to the soil would take many times the material of the plant 

 itself. The same thing is effected in others of this class by long 

 petioles and stems which being pliable allow the leaves to float on 

 the water, for if attached stiffly to the stem the running stream 

 would tilt the leaf towards its downward course, and by being long- 

 er than absolutely necessary, it allows the leaf to surmount the rise 

 of a stream as well as to follow it in its fall. The same remarks ap- 

 ply to the pliability of stems which having immersed leaves must 

 still effect the elevation of their supplementary floating (Potttmo- 

 <jeton) or aerial (Nasturtium lapustre) leaves, which would other- 

 wise not perform their functions. Floating leaves are generally entire 

 and simple in form to aid their floating; this is supplemented in 

 Nymphcea regia by the raised border of the leaf. 



Immersed leaves are long and linear (Potamogeton, Vallisneria) 

 or divided into coarse or capillary segments. These leaves must re- 

 main in the water, since out of it they cannot live and also have no 

 stomata to breathe with. So we find arrangements to keep them in 

 the water as long as there is any; the leaves are flaccid or the stem 

 may be weak, and so they rise and fall with the height of the water 

 (some immersed Potamogetons and Vallisneria.) The two cases 

 are often correlated in capillary leaves, Utricularia and Ranuncu- 

 lus aquatilis, var. trichophyllus% while in other specimens^ these 

 leaves 1 may be stiff, depending on the flexible 'stem entirely (Nastur- 

 tium lacustre and Ranunculus aqmtilis, v:.r. stagnatilis). Since these 

 plants breathe in the water and the amount of surface exposed is an 

 item for them, we find capillary division abounding among immers- 

 ed leaves. But while aerial leaves have strong fibers to spread out 

 the leaf to the best possible advantage this is effected in water 

 plants by large air holes in the leaf; this may explain their flaccid- 



ness a 1 so. 



Plants having stomata supplemented by large air tubes may 

 lerd a double existence, living first in water, and later on the dried- 

 up bottoms of pond or stream as in Isoetes and perhaps Vallisneria 

 septangulare, Elatine, &c. Is not this principle of the uses of 

 leaves 'a more complete key to these facts than that of changing 

 currents? 



(See in this connection "Designs of some leaf-forms" in the 

 March No. of the Torrey Bulletin.)— Aug. F. Foebste, Dayton, 0. 



Recently Introduced Plants in and al.out RocMord. Ill — 



The rapidity with which our thriving western cities run through 



