CONIPBRALBS 



61 



discoid ones closely imbricated and appressed upon tlie axis 

 (" concrescent "), as in many of the Cupresseae, to the charac- 

 teristic free needles of the Abieteae, and the broad blades of 

 certain Podocarpeae (Figs. 44^46, 53). In general the phyllo- 

 taxy is spiral, but in the Cupresseae it is cyclic. The foliage 



Pig. 45. — Phyllocladus spp. : A, branch with staminate strohili ; a, ataminate strobilus ; 

 b and c, sporophylls from a ; d, longitudinal section of ovulate strobilus ; «, mature 

 ovulate strobilus ; /, longitudinal section of « ; 5 and g, ovulate branches. A and 

 a-d^ P, trichomanoides^ after Hooker ; e and /", P, rhomboidalis^ after Eichard ; B 

 and g, P. glaum. — Entire plate from Engleb and Prantl's Nat. Pflanzenfara. 



leaves are very persistent, enduring from one to ten years, the 

 basal growth permitting them to increase in size at base with 

 the increase in the diameter of the axis. So far as recorded, 

 the only Conifers with deciduous leaves are Larix, Taxodium 

 distichum, and Glyptostrobus, a habit which seems to be a de- 

 rived one, as in the juvenile forms of Larix the leaves persist 

 through the winter. 



The histology of the foliage leaf reveals a very xerophytic 

 structure, and argues for adaptation to extreme conditions. The 

 epidermis consists of elongated, iiberlike cells, with strongly 

 cutinized walls, the guard cells being deeply sunken. The 

 rigidity is chiefly due to the hypodermal layers or masses of 

 elongated sclerenchymatous cells. In case the leaf is flat the 

 mesophyll differentiates into the palisade and spongy regions, 

 but if it is acicular the mesophyll is uniform throughout; in 

 any case there are curious platelike " infoldings " of the wall. 

 In the acicular leaves there is a single central bundle region, 



