136 



ECONOMIC WOODS OF THE UNITED STATES 



more than 100. Within the same species, however, the variation 

 is within narrower limits, though the number is never constant. 

 In Magnolia and Liriodendron, for example, the number of bars is 

 usually less than 15 and the spaces are wide, while in Ilex, Nyssa, 

 and Liquidambar the bars are much more numerous and are closely 

 spaced. 



In the following table are listed the genera of native woods in 

 which the vessel perforations are exclusively scalariform. In a 

 few cases, perhaps, simple perforations will occasionally be found 

 in association with the predominant type. The list is believed to 

 be complete so far as the trees are concerned but not for the shrubs. 

 Eight of the genera yield wood of commercial importance. It will 

 be noted that no ring-porous wood is included. Scalariform per- 

 forations are never found in large vessels, such for instance as are 

 individually distinct to the unaided eye, presumably because the 

 presence of gratings would interfere with the function of large 

 vessels, namely, the rapid conduction of water in quantity. Solere- 

 der calls attention to "the striking fact that the occurrence of 

 scalariform perforations in the vessel often goes hand in hand with 

 small lumina and the presence of bordered pits on the prosen- 

 chyma." (Systematic Anatomy of the Dicotyledons, p. 1138.) 



TABLE VIII 

 Indigenous Woods with Vessel Perforations Exclusively Scalariform 



AqUIFOLIACEjE 



Ilex 

 Betulace^; 

 Betula 

 Alnus 

 Corylus 



CaPRIFOLIACEjE 



Viburnum 



CORNACEjE 



Cornus 



Nyssa 

 Cyrillace.e 



Cyrilla 



Cliftonia 

 Ericaceae 



Rhododendron 



Kalmia 



Vaecinium 



Andromeda 

 Hamamelidace^j 



Liquidambar 



Hamamelis 



Magnoliace^e 



Liriodendron 



Magnolia (mostly) 

 Myricace^e 



Myrica* 

 Myrtace^e 



Eugenia 



RfflZOPHORACEiE 



Rhizophora 



SaXIFRAGACEjE 



Philadelphus 



Hydrangea 



Ribes 



SyMPLOCACEjE 



Symplocos 



Staphyleace^b 



Staphylea 



StyraCEjE 



Mohrodendron 

 Theace^ 

 Gordonia 



* Some simple perforations present in Myrica cali/ornica. 



