ANATOMY AND PHYXOGEN"Y OF THE CONIFERALES. 



27 



Penhallow ( :03) assumes that the occurrence of these ray tracheids marks a high stage 

 of evolution in the genera which are characterized by their presence. It should be 

 remembered in this connection, as Strasburger ('72) has emphasized, thai the Conif- 

 erales are a group which has undergone regressive metamorphosis and jis a consequence 

 structural features of high complexity are more apt to be characteristic of the ancestral 

 tonus than of those of more modern origin. Further, Penhallow (:03) himself has called 

 attention to the fact of the sporadic occurrence of ray tracheids in the genera Juniperus 

 [J. communis, var. alpina) and Cupressus (C. thyoides and nootkatensis) among the 

 Cupressineae. Their presence here is to be interpreted rather as vestigial than rudi- 

 mentary especially in view of the peculiarities of the seedlings in this group, which seem 

 to show clearly that it is a reduced order of the Coniferales. Furthermore, the occur- 

 rence of ray tracheids is in itself by no means an indication that the Abietineae are a 

 modern order, for the same feature was present in that very ancient family, the Lepido- 

 dendraceae, which, as has been pointed out by Corda (Williamson, '81, p. 21)4) and Scott 

 (:00), was characterized by the presence of scalariform tracheids in the medullary rays. 



We may now pass on to consider the closer affinities of the several genera of the 

 Abietineae. As has been pointed out above they fall naturally into two series as a result 

 of the consideration both of their anatomy and of their reproductive organs. The genus 

 Pinus appears to stand by itself among the Pineae, for its fascicled leaves and altogether 

 unique cones, as well as its great geological age, separate it clearly from the other three 

 genera. Picea and Pseudotsuga seem to be rather close to one another, but Larix cannot 

 be regarded as far removed. The genus Abies includes perhaps the greatest number of 

 primitive features among the Abieteae. Closely allied to it is Pseudolarix, not only 

 in its anatomical structure and its rapidly deciduous cone scales but also in its thickly 

 integumented seeds. The deciduous foliage of Pseudolarix is by no means sufficient to 

 unite it with Larix, as is generally assumed by the taxonomist, for Cedrus, which has 

 always been regarded as possessing close affinities with Abies, is also occasionally decidu- 

 ous, as has been pointed out by Carriere and Kent (:00) . Abies and Pseudolarix closely 

 resemble each other in the possession of very characteristic mucilage cells, which are 

 quite absent in Cedrus and Tsuga. Cedrus is generally conceded to be allied to Abies, 

 to which, as has been shown above, it presents a very close resemblance in the details 

 of its anatomy, the structure of its seeds, and the deciduousness of its cone scales. 

 It differs from Abies and Pseudolarix in the absence of mucilage cells. Of the four 

 genera of the Abieteae, Tsuga shows the least affinity with the others. Its cone scales 

 are not deciduous and its seeds are not relatively as thick walled as those of the three 

 first mentioned genera. Further, in the single resin canal of the leaf, it resembles many 

 of the Cupressineae. 



