3(H) PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
Iridaceae: Sisyrinchium angustifolium. 
Araceae : Acorus Calamus ; Anthurium and many other genera 
(Oudemans, Leitgeb). 
Cannaceae: Canna indica. 
Ranunculaceae : Panunculus bulbosus. 
Saxifragaceae : Parnassia palustris. 
Haloragidaceae : Myriophyllum ambiguum * 
Primnlaceae: Primula auricula, P. elatior , P. officinalis , Glaux 
maritima , Trientalis europaea, Lysimachia vulgaris, L. 
stricta* 
Scrophulariaceae : Scrophularia nodosa , Gratiola officinalis. 
Labiatae : Mimulus ringens * 
Gentianaceae : Erythraea vulgaris, E. centaurium. 
Asclepiadaceae: Hoya carnosa, Cynanchum vincetoxicum, Ascle- 
pias curassavica. 
Valerianaceae : Vcderiana officinalis. 
Concluding Remarks. 
In the foregoing pages an interesting structure of the piliferous 
layer has been shown to be characteristic of most Pteridophytes 
above the ferns (it is found in a small group of the true ferns also) 
and of a large number of Monocotyledonous orders. In still other 
orders of Monocotyledons essentially the same structure is found, 
but occurs in an underlying layer. The question may be asked 
whether any inferences can be drawn as to the phylogenetic deriva¬ 
tion of this structure, considered as a Monocotyledonous character. 
The suggestion occurs that the structure under discussion may be 
merely adaptive and locally developed, in a systematic sense ; that 
it is of no more systematic worth than such features as large inter¬ 
cellular spaces and reduction of stereome occurring in aquatic plants 
of various unrelated groups, or as multiplication of the epidermal 
layers of the root, characteristic of widely separated epiphytes ; and 
that, in particular, the given structure may be due, in the plants in 
which it obtains, to the relation of the root to the presence of water. 
This view, however, seems not to be supported by the facts of 
distribution. Many of the species are hydrophytic, or at least 
semiaquatic; but perhaps as many others are mesophytic and not 
