122 



llOBERT TRACY JACKSON ON 



are primaries, but in Fig. 89 it is seen that character leaves develop early, and at 

 al>()ut the same period of growth, both on the terminal shoot and side branches. Side 

 branches bear a few whorls of primary leaves in fours: but ver}^ soon the later form of 

 leaf is introduced. The leaves of this late nepionic stage are appressed, sharp-pointed 

 (PL 22, fig. 89a), arranged in four-leaved whorls, the marginal leaves narrow, elongate, 

 and embracing the median pair. The arrangement is similar to that of Thuya, Fig. 84b, 

 but with the essenti;il difference that in Thuya the leaves are two-ranked and marginal 

 leaves embrace the edo;es of the leaves of the next succeeding wdiorl. In adult Libo- 

 cedrus decurrens (Fig. 90) the leaves are appressed, blunt distally, and in four-leaved 

 whorls as in the later stages in the j'onng. 



The variations in the seedlings are ([uite striking. Out of twenty-five specimens, 

 22 conformed to the type as described. Two specimens had skipped the two-leaved stage, 

 the first whorl of leaves after the cotyledons being a four-leaved whorl (Fig. 11, and PI. 



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9-11. Plan.s of ccimiiarativp pliyllotactic arrangement of cotyledons, c, and first two whorls of nepionic leaves, 1, 2. 



9. Typical arrangement, in which there are two leaves in the first nepionic whorl and four leaves in the second 

 nepionic whoi-1, seen in 1*1. 22, figs. 88, 80.] 



10. Abnormal arrangement in wliicli tliere arc only two leaves in tlie second nepionic whorl, seen in PI. 22. fig. 92. 



11. Abnormal arrangement in wliicli there are four leaves in tlie first as well as in the second nepionic whorl, seen 

 in ri. 22, fig. 91, 91a. 



22, Figs. 91, 91a) . It is noteworthy in botli of these specimens that the two leaves of 

 either side are fused proximally and for a slight distance (2 mm.) upward from their 

 point of insertion on the stem (Figs. 91,91a). This suggests the view that the four- 



