278 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
the character of the epidermis of the root. The cells composing the 
superficial tissue in any given root are of generally uniform appear¬ 
ance in the younger stages. Root-hairs arise indiscriminately from 
all or any of the cells, after cell division has ceased and the cells 
have elongated. While the structural peculiarities to be found in 
Brasenia, Cabomba, Nuphar, and Nymphaea are probably attributa¬ 
ble indirectly to the aquatic habit, it is instructive to find that aside 
from the genera named, none of the numerous aquatic Dicotyledons 
studied exhibits the same modifications. 
The species which have been examined, arranged under the fam¬ 
ilies to which they belong, are as follows: — 
Casuarinifiorae : Casuarina equisetifolia. 
Urticifiorae : TJrtica dioica, Cannabis sativa. 
Polygoniflorae : Peperomia sp., Polygonum Muhlenbergii , Rumex 
Acetosella. 
Curvembryae: Beta vulgaris, Buda marina, Dianthus Caryo- 
phyllus, Salicornia herbacea , Spinacea oleracea, Sueda 
linearis . 
Polycarpicae : Ranunculus aquatilis var. trichophyllus. 
Rhoeadinae: Cardamine hirsuta, Nasturtium officinale, Papaver sp. 
Cistiflorae: Prosera rotundifolia, P. intermedia , Elatine ameri- 
cctna, Sarracenia hybrid, Viola blanda, V. primulaefolia. 
Gruinales : Linum flavum, Oxalis sp. 
Tricoccae : Callitriche verna, Euphorbia Poinsettia. 
Aesculinae: Acer saccharinum. 
Frangulinae: Vitis sp. 
Thymelaeinae: Grevillea sp. 
Saxifraginae: Bryophyllum calycinum , Chrysosplenium america- 
num. 
Rosiflorae : Rubus sp., Spiraea astilbeoides. 
Leguminosae: Phaseolus mdgaris. 
Passiflorinae : Bego?iia Rex , B. metallica. 
Myrtiflorae : Ludwigia Mullertii, Lythrum Salicaria, Myriophyl- 
lum ambiguum , Proserpinaca palustris , P. pectinacea. 
Umbelliflorae: Paucus Carota, Cicuta sp. 
Hysterophyta: Aristolochia elegans. 
Primulinae : Lysimacliia stricta. 
Personatae: Pinguicula lutea, Mimulus ringens, Strobilanthes 
Pyerianus , Veronica scutellata. 
