358 Mr. J. Miers on the Nature and Origin 



progress of the increment that occurs, from the earliest period 

 of the growth of the ovule, to the final ripening of the seed. 

 The most important inference I have there deduced, is, that the 

 external coating of the seed in which the vessels of the raphe 

 are imbedded, derives its origin, not from that which should be 

 considered as the true primine, or outer original tunic of the 

 nucleus, but from an extraneous sac that subsequently grows 

 over that tunic, and which is developed from its funicular sup- 

 port, which I have termed the placentary sheath : in confirma- 

 tion of this inference, I now proceed to show the manner in 

 which this growth is efi'ected. Wishing to submit the truth of 

 this deduction to the test of observation, I examined lately the 

 growth of the ovule of the Almond, as that is the instance to 

 which I referred, showing the manner in which the vessels of 

 the raphe become distributed over the whole area of its seminal 

 tunic : the result proves the correctness of my inference in regard 

 to the nature and origin of the external coating first mentioned, 

 for I had previously no evidence to demonstrate how and when 

 it was produced. 



At the earliest stage observed in the cell of the ovary, the 

 placenta throws out two small bracket-like protuberances, each 

 being the germ of a placentary sheath, and near its extremity 

 there is seen to sprout a small mammillary knob, which is the 

 rudiment of the nucleus : this nucleus, continuing to grow, is 

 soon surrounded at the point of its origin by two small cups : 

 by degrees, the surface of the sheath on which these cups rest 

 becomes channeled, and then more deeply grooved ; at which 

 period we may discern, within the body of the sheath, the 

 nourishing vessels essential to the growth of the ovule, proceed- 

 ing from the placenta and terminating at the point where the 

 nucleus and its distinct cups are attached to it, which point I 

 have called the gangylode. The grooved surface of this support 

 now continues to extend, not at its margin, which scarcely in- 

 creases, but by the growth of its middle portion, which, expand- 

 ing downwards, forms at first a shallow, and gradually a deep 

 cup, in the progressive manner shown in the marginal figures 

 (fig. 1), until at length we see it formed into an oblong open 

 pouch, within which is seated the nucleus, partly enclosed in its 

 proper tunics : during this transformation, it will be observed 

 that the margin of the grooved channel of the ovular support, 

 which now becomes the mouth of the pouch, has never changed 

 its original position, remaining on the same level, and in the 

 same contiguity to the placentary point, out of which the sup- 

 port first issued. Here we see produced what is termed an 

 inverted or anatropal ovule : it is, however, important to observe, 

 that in this action the ovule undergoes no inversion whatever ; 



