SPERM ATOPHYTA 71 



(2) PhiacecB. — With dry seeds and ovules covered by scales. 

 These include four tribes : — 



(a) AraucaricB. — A group that is now mainly restricted to 

 a small region of the southern hemisphere — Norfolk Island, 

 Brazil, southwestern Argentina and Chili, but widely distrib- 

 uted during the Mesozoic, being abundant in the Jurassic 

 rocks of Great Britain, Spitzbergen, South Africa, Australia, 

 India, the eastern United States, and in the Antarctic regions. 

 A comparison of the former and the present distribution of such 

 a genus is of vivid interest as indicating former geographic 

 connections which are now severed. 



From the association of fragments of petrified araucarian 

 wood with the jet at Whitby, England, it may be supposed that 



Fig. 24. — Transverse section ( X 60) through an annual ring of the Tertiar\ conifer, 

 Sequoia magnifica Knowlton. sp., cells added during spring or wet season when 

 an abundance of moisture caused rapid growth, hence large cells; su., cells added 

 during summer or dry season ; the cells here are small. The change is gradual from 

 the moist spring to the succeeding dry season, but the next spring's growth begins 

 suddenly, hence here is a very sharp change in size of cells. These more or less 

 sudden changes produce the annual ring, merely a contrast in size of cells, con- 

 trasting periods of slow and rapid growth. (From Knowlton.) 



some of the jet, at least, consists of the fossilized remains of the 

 wood of Araucaria. 



(6) Abietcc. — The group of the more common evergreens, — 



