330 ON NAIAS GRAMINEA DEL., VAR. DELILEI MAGNUS. 
that another set had them; that is, that the one set belong to the 
var. Delilei, while the other agrees with the form which appears in 
Cordofan, Djur, Algiers, &c. This would appear to be a clear 
proof that the oases of the Libyan Desert have received their flora 
from Egypt as well as from Central Africa. This agrees with the 
results of the investigations which Ascherson furnished to the 
‘ Botanische Zeitung ’ for 1874, pages 641 to 644. 
ese explanations would, however, seem to be somewhat 
contradictory, seeing that the English specimens are remarkable 
for their great length of leaf, whereas the leaves of N. graminea 
from Cairo and Damietta are very short. But a minute examina- 
tion of form teaches us that we must not attach much importance 
dener, in his exhaustive work, ‘The Mechanical Principle in the 
Anatomical Construction of Monocotyledons,’ Leipzig, 1874, page 
122, remarking that Potamogeton fluitans in its customary habitat 
of running water has a developed system of bark-bundles, whereas 
the var. 8 stagnalis Koch is completely deprived of same. 
“The var. Delilei, found in the stagnant waters of the 
ov erflowed Nile, is a most persistent and constant one, as during & 
gl & = 
constancy and total independence of habitats, whilst its formation 
has probably been caused by the same.” 
It now only remains to me to tender my acknowledgments to 
Mr. Ridley, Mr. Arthur Bennett, Dr. Magnus, Professor Ascherson, 
Mr. Beeby, and to the Editor of this Journal, for help rendered. 
The delay which has occurred in completing this paper has been 
— it has had to take its turn in the intervals of a busy 
ife. 
