12 



FAMILIES OF FLOWERING PLANTS. 



trees growing in such situations, and illustrates an adaptation to envi- 

 ronment of which plant life furnished so many interesting examples. 

 The purpose of the knees is not only to furnish the tree with props, 



Pig. 8. — Tamarack swamp with horder of sedges. (From MacMillan's •Minnesola Plaut Life" 

 by courtesy of the authorj. 



but to admit air to the roots, as is proven })y the fact that the trees 

 are frequently killed when flooded above the tops of the knees. 



Tribe Cupressineae. — Nine genera, the species of which are very 

 widely distributed. The most important are CalHtrts, with 15 Afri- 

 can and Australian species; Lihocedriis, Avith S species in America and 

 New Caledonia; ( '>ij)rc.ssi{><, with 12 widely scattered species; Cluim- 

 (tcyjjaris, wdth •! in North America and Japan; and Juniperus, contain- 

 ing 80 species, distributed throughout the whole temperate zone. Sev- 

 eral species of Chainawcypaius, particularly the Lawson's cypress 

 (6'. Latr.soniana) and the yellow cypress [C. JWtkaensis) both occur- 

 ring on the Pacific coast, are valued both as timber trees and as orna- 

 mental shrubs in cultivation. Oup7'essus and Lihocedrus. also furnish 

 valuable timber. An African species of CaUitris, the sandarac tree, 

 yields sandarac, which is a white resin, used both as an incense and in 



