210 LEMNACEZ. 
attachments of the flowers to the spatha a structure which 
will only be explained by a gradation of intermediate struc- 
tures. 
It is easily explained by an assumption of the adherence of 
the spadix to the midrib of the spatha. And this is the 
more natural, both from analogy and because from the struc- 
ture of the peduncle it is evident that in Aroideæ it is 
itself an axis, of which the spadix is the continuation. In 
Pothine this is most obvious; in Acoroidez again it is less 
80. 
It agrees with them in the composition of its ovary, and 
with many ovula of the order. 
It differs in lower organisation, in the cup surrounding the 
pedicel of the male flowers, (which is obviously a higher 
— of the intermediate body,) and above all, in its 
germination. 
The Moris of the radicles of the roots have the same 
origin as those of Lemna, and is derived from the central tis- 
sue, the outer tissue being of course perforated, but the sheath 
derived from this never exceeds the size of a cap, and is deci- 
uous. 
From the lowest plants of Aroidez the circle of natural 
affinities would pass through Pistia, and close by Lemnacez, 
in which the hypogynous structure of Pothos etc. is reverted 
to. 
In organs of aération Pistia differs but little from ordi- 
пагу Aroidee. There is perhaps a tendency to the usually 
precise regularity of axillary development of buds, like 
others Aroidez, the buds are enclosed membranous. 
* Pistia stratiolis. This plant is much more developed than Lemna, 
with which it can searcely be associated. It throws a good deal of light 
on the nature of the spatha of Aroidea, the lamina of which evidently 
belongs to the peduncle of the spadix. It affordsa beautiful instance 
of the uniformity of nature, the green body situated between the female 
flower, and the male representing the abortive ones of such common 
occurrence in the order 
