270 
is exceedingly difficult to prove they are not, without years of careful 
work. I have myself made bees produce hybrids between l’erbas- 
cum floccosum, and V. Thapsus, L., and when these hybrids flow- 
ered I found the bees showed evident preference for their flowers, 
over those of either parent. In Potamogeton I have attempted to 
hybridize with several species, but as yet without success. I have 
had plants named as continental hybrids for Britain, one of whose 
supposed parents does not exist as an indigenous species (or other- 
wise ?) in our own country ; this is met by the hybrid-man by sup- 
posing that its parent did exist but has died out. Geology clearly 
tells us that many species did exist in many parts where they cer- 
tainly are not known to exist now, so here again we have a diffi- 
culty to find an adequate answer, and the query of proof is greater 
still. Within easy walk of my home Potamogeton densus, P. per- 
foliatus and P. crispus grow in a mill-head, and adjacent stream in 
beds intermixed, yet for twenty years I have never seen a speci- 
men that I could not refer with safety to either species. The 
water is in rather rapid movement, I admit, and doubtless a still 
ditch or pond would be more likely to produce hybrids, especially 
if teeming with pond-life; but the fact remains that the three 
species are in actual and continuous contact. 
After hybrids, the question of species naturally occurs to one. 
No one ever has, and probably never will, be able to define what 
constitutes a species. Mr. H. C. Watson, in his various works on 
the geographical distribution of the British Flora, attacks the 
species maker very severely, but he owns it is because it interferes 
with the collation of other Floras, and with the certainty of the 
plants so-called being separated by other botanists, and so leading 
to errors in recorded distribution. The difference between 4 
species of Bentham, and one of Gandoger is very great, and while 
the one overlooks natural distinctions, the other creates impossible 
differences. Looking through Dr. Morong’s Monograph with 
these matters before one, what seems to present itself, is; that in 
the other genera, such as Ruppia, and Zannichellia, Dr. Morong 
is less given to divide than in Pofamogeton, yet if we carefully 
contrast the characters of P. pectinatus, and P. latifolius, Morong, 
they seem less striking than those between some of the above _ 
named two genera. 
