LOCALIZED STAGES IN DEVELOPMENT. 123 



leaved condition of this individual whorl is morphologically a splitting of the normal two 

 leaves characteristic of this stage. In relative phyllotactic arrangement this first whorl 

 in relation to the cotyledons occupies a similar position to the second whorl of the 

 normal growth; compare Figs. 9 and 11. The second whorl occupies the same position 

 as the third whorl in nornuvl growth. 



The second specimen mentioned as having a four-leaved whorl succeeding the 

 cotyledons has an arrangement as in Fig. 91, excepting that the third whorl above the 

 cotyledons consists of an isolated two-leaved whorl and is the only such variation 

 observed. 



A third specimen showing variation from the normal is represented in PI. 22, fig. 

 92. In this all the primary leaves are two- instead of four-ranked ; but the later char- 

 acter leaves are four-ranked as usual. The first pair of leaves alternates with the cotyle- 

 dons as usual. The second pair alternates with the first and overlies the cotyledons, Fig. 

 10. Succeeding pairs of primary leaves are regularly alternated (PI. 22, fig. 92). The 

 phyllotactic arrangement of leaves in the normal and aberrant seedling is seen by com- 

 paring Figs. 9-11. The varying arrangement of the leaves in these several seedlings 

 shows how sensitive the growth force of these plants is to the relations of environment, 

 each set being arranged so that the first whorl alternates with the cotyledons and the 

 second whorl alternates with the fii'st, covering the cotyledons or not as the case may be. 



Youthful characters are considered of phylogenetic significance, barring larval 

 adaptation and skipping of stages by acceleration of development. It is seen that 

 in the young of Juuiperus, Thuya, and Libocedrus, succeeding the cotyledons there 

 is typically a whorl of two leaves, succeeded by one or more whorls of four leaves. In 

 Ciqyresi^us lawsoniana Murray, according to the figure in Professoi- Sargent's Silva, the 

 nepionic leaves are all in whorls of fours. These should point to primitive radicals 

 which in the adult condition are characterized by a similar arrangement. Of the two- 

 leaved stage no ancestral form can be pointed out at present. It would seem that 

 Thuya, Cupressus, and Juuiperus may be considered degradational types which in the 

 adult in t3q:)ical S23ecies have reverted to the two-leaved type characteristic of some 

 ancestral form, as evinced by stages of their own young. The degradational character 

 of these genera is evinced by the depauperate scale-like leaves as well as the two-ranked 

 arrangement. The adult representative of the young four-leaved stage of these genera, 

 it seems, may be represented by the type Libocedrus or more properly a predecessor of 

 the same, which had fiDur-ranked needle-like leaves. Libocedrus is not known earlier 

 than the Cretaceous, and these old forms are quite close to the modern representative, 

 but its four-ranked arrangement is so striking that it would seem to indicate that it is 

 in the line of ancestry of the associated genera. 



