Natural Family of Plants called Coniferse. 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 Abietinece, we must, I think, admit that the remarkable organ 

 in the present genus is really a pericarpium. In Pinus (Picea) hracteata, 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 placentae 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- 

 carpial 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 imhricata, 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 aflFords the most convincing proof 

 of the origin of the supposed placentae ; for in the diflferent 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 perictirpia. — ^See Appendix to 

 Capt. King's Voyage, vol. ii. p. 560. 



