376 ON THE FROND-CELLS OF LEMNA AND WOLFFIA. 
1865, and * Quarterly Journal of Microscopical Science,’ Jan. 1866,— 
have shown the great value of the anatomy and physiology of the cells 
as diagnostic characters in allied Orders, and even species, of all the 
different classes of flowering plants and,some Ferns; while, among 
numberless other proofs that raphis-bearing is a constant and intrinsic 
character of the cell-life of certain plants, I have, as concerns our British 
Duckweeds, been for years insisting on the regular richness of some 
species and penury of others in raphides, although the plants thus 
differing grow close together under the very same conditions. 
And now a still more remarkable difference appears between Wolffia 
arrhiza and Lemna minor ; for while, as I have long since shown (Ann. 
Nat. Hist., May, 1861), this Lemna is one of the species in which 
raphides most abound, they cannot be detected at all in the Wolfia, as 
may be easily witnessed, either in thin horizontal sections of the fronds, 
or in fragments thereof detached by needles. As this curious diagnostic 
has not, I believe, been described or figured, a sketch of the mere out- 
lines is now prepared for Dr. Seemann’s * Journal of Botany ;’ and this 
chiefly to show the fitness of extending similar observations to all the 
allied species. 
1. Parenchyma-cells of Wolfia arrhiza. 
2. Parenchyma-cells and bundles of raphides of Lemna minor. 
Further examinations should also be made of Wolfia arrhiza, now 
an easy task, since the interesting addition, by Dr. Trimen, of this 
plant to the British Flora, ante, p. 219 ; and such inquiry is the more 
