MR. JOHN MIERS ON THE LOASACEZÆ. 229 
three nerve-like lines of parietal placentation : the ovule at this stage much resembles 
the seed in shape, but is without any constriction; the outer delicate lax integument, 
very elongated and attenuated at each extremity, shows in its middle an oblong body of 
denser texture, as before mentioned: the only circumstance worthy of note is, however, 
of some value, as we here ascertain the position of the hilar point of suspension, which 
is at the upper extremity; and from this we learn its relation to the direction of the 
embryo, which is not to be detected in the ripe seed taken from a capsule after 
desiccation. 
The foregoing details naturally suggest the inquiry, What is the nature of these 
sminal envelopes, which, in an anatropous seed, exhibit neither a raphe nor a chalaza ? 
Iam aware that many botanists will regard this question as too trivial in its nature 
to merit discussion, and will consider the condition of the seminal tunics of no import- 
ance in a practical point of view, because it affords them little assistance in determining 
the genus or species to which any plant may belong. On the other hand, any condition 
of the seminal tunics at variance with the ordinary rule of development becomes a matter 
of extreme interest to those who have made physiological botany their study; they will, 
of course, endeavour to ascertain the cause of the want of the usual organic connexion 
between the two integuments above mentioned, as well as of the total absence of those 
nourishing vessels, which ordinarily extend from the placenta to the chalazal base of the 
seminal coatings, and which we have been taught to believe are essentially necessary to 
the development and growth of seeds. | 
There can be no doubt of the facts above stated ; and it is of some importance to know 
that it is not à solitary instance, for I find the same cireumstances repeated under still 
more manifest conditions in other genera of the same family. In Bartonia, for example, 
the seed is very different in form and appearance; it is orbieular, extremely compressed, 
Vith a central opake disk, surrounded by a delicately reticulated translucid wing, from 
à point on the margin of which it is attached to the placenta in a horizontal position. 
By introducing the point of a knife into the margin of this wing, and carrying it round 
" circumference, it becomes divided into two platter-shaped halves, thus showing the 
‘ing to be a portion of an entire, flattened, integumental sae, enclosing an opake body 
m the hollow of the discoidal central space, where it rests without the appearance of any 
attachment whatever between it and the sac; there is only a deposit of loose cellular 
tissue between them, in the form of opake-white granules. When viewed under a 
microscope, this delicate outer integument appears uniformly and finely reticulated ; P? 
Fette] of any kind, no cicatrix, no trace of either raphe or chalaza, no indication of any 
organic connexion between it and its enclosed disk can be detected : the central disk- 
: body is formed of an extremely thin mass of albumen, covered by a colourless pel- 
membrane, too delicate to be detached in an entire state ; and though both are very 
not fai] t, they show no trace of vessels of any kind; were they present, they could 
iro to be detected in membranes of such great tenuity. The albumen — an 
the , with a terete radicle pointing to the remote placentary point of attachmen ” 
to E of the seed; the cotyledons are flat and orbicular, their diameter being e 
* length, and twice the thickness, of the radicle. We may contrast this structure 
* 
