Natural Family of Plants called Coniferæ. 169 
Dr. Schleiden in support of his theory, it would be premature to enter into a 
full discussion of the subject upon this occasion ; but whatever may prove to 
be the case in Abietineæ, we must, I think, admit that the remarkable organ 
in the present genus is really a pericarpium. In Pinus (Picea) bracteata, for 
example, these supposed pericarpia do not differ from the ordinary leaves ; and 
in some other species the transition from them to leaves is imperceptible, the 
exterior ones being in most cases barren. The supposed placentæ present 
a foliaceous character in Abies and Larix, and in the Silver Firs, where the 
leaves are petiolate, the scales are constantly stipitate, and in all cases they 
follow the arrangement of the foliaceous organs, which, I think, would not be 
so uniformly the case were they portions of the axis, and not modifications 
of the leaves. This is beautifully shown in the following genus Athrotaxis, 
where the female spike presents all the appearance of a young branch. 
In Cunninghamia and Araucaria we have only one organ present, which is 
clearly derived from the leaf, and which performs the office of the supposed 
placenta in Pinus, in the former genus bearing several ovula, and in Araucaria 
one only, with which it becomes confluent. The existence of a single floral 
envelope in these two genera may be accounted for either by supposing that 
the bracte and pericarpial leaf become confluent at an early period, or that 
what I have described as the bracte and pericarpium may constitute in all 
cases but one organ, the scale being merely the enlarged base of the peri- 
carpiál leaf; a view which would gain some support from the change which 
takes place in the leaves of diseased branches of the spruce fir. Pavon, in his 
memoir on Araucaria imbricata, describes and figures the free extremities of 
the pericarpial leaf and the wing of the ovulum, which are readily distinguish- 
able in the young state, as a bivalved stigma. 
Perhaps the genus Callitris of all others affords the most convincing proof 
of the origin of the supposed placentæ ; for in the different species of that 
genus we uniformly find them regulated by the number of leaves in a verticil, 
which consists of three or four. 
All these circumstances appear to confirm the accuracy of the view taken 
by Mr. Brown* that the scales are expanded pericarpia; and it seems more 
* In justice, however, to this learned botanist, I ought to state that he was the first to suggest the 
very theory adopted by Dr. Schleiden as to the nature of the supposed pericarpia.—See Appendix to 
Capt. King's Voyage, vol. ii. p. 560. 
