CHAP. II. 
OVULE. 
‘219 
clearly understood what he saw, and that the best account of 
the ovule is given by Fritzsche in Wiegmann’s Archiv. : that, 
in many plants, the ovule has but one integument, as in 
Coniferae, Compositae, Lobeliaceae, Gentianaceae, &c. ; and in 
others two, as in Polygonaceae, Cistaceae, Urticaceae, Araceae, 
and all other endogens, &c. He also appears to deny the 
existence of a tercine, as he expressly does that of a quartine ; 
and I do not clearly understand whether he regards the 
quintine as belonging to the pollen tube, or as being the sac 
of the amnios, as it surely is. He moreover finds that while 
all endogens have two integuments of the ovule, the majority 
of monopetalous exogens have but one, whilst the polype- 
talous usually possess two. Schleiden states that “ the plan 
which nature adopts is simply this : — The example I shall 
select is that of the atropous ovule, for instance of the Poly- 
gonaceae, as being the most simple. At a certain distance 
below the apex of the original protuberance an ideal line 
may be recognised, intended as the basis of the nucleus, 
which does not afterwards increase in thickness. Above 
this line the apex forms itself into the nucleus, and below 
it the substance of the axis expands and forms a protube- 
rance, which extending itself as a kind of membranous 
fold gradually covers in the nucleus (Integumentum pri- 
mura aut internum^ mihi ; Secundine^ Mirb. ; Membrana in- 
terna, Auct.). Sometimes soon after, and indeed almost 
contemporaneously with this, sometimes later, sometimes 
immediately below the first protuberance, at other times 
at some distance from it (as, for instance, in many Polygo- 
naceae and Cistaceae), we may next observe a second pro- 
tuberance, which, as the second integument, covers in the 
first [Integumentum secundum sive externum, mihi ; Primine, 
Mirb. ; Testa, Auct.). The first-formed integument cer- 
tainly does frequently consist only of a fold of the epider- 
mis of the nucleus ; nevertheless, we find a tolerably thick 
parenchyma taking part in its formation in almost all those 
families which form no second integument, and also in somie 
which possess both coverings, as, for instance, in the Euphor- 
biaceae, Cistaceae, and Thymelaceae. In the case of these three 
families, a peculiar process takes place; namely, upon the 
