COMMENTS ON TERMINOLOGY 351 



Broken — .5 to .8. G., dicht. F., dense. 



Medium — .?> to .5. G., luckig. F., entrecoupe. 



Open — below .3. G., licht. F., clair. 



See Crown density and Shade density. 



Shade density. The complement of the percentage of light passing through the 



crowns, assuming unbroken light to have, at the time of measurement, a value of 



100 per cent. The measurement is ordinarily taken at a standard height of 43/2 



feet, and represents the conditions of growth for reproduction at a lesser height. 



See Crown density and Crown closure. 



Per now: 



The point is well taken, and a revision needed. There are, however, 

 clearly three conditions involved : 



1. Density of the individual crown, a biological factor, being in 

 part specific, in part result of site. This appears to me well covered 

 by the term "crown density." It remains to secure a photometric 

 standard and grades for it. 



2. Area shaded by crowns, a physical or mathematical factor, 

 hitherto involved under the term "crown density" ; perhaps best termed 

 simply "crown area," the sum of the individual crown areas related to 

 the unit of area in decimals, as customary. 



3. The total shading efficiency, a function of 1 and 2 com- 

 bined, for which, in order not to introduce a new term, "crown cover" 

 would be an expressive term; a photometric coefficient based on relative 

 tolerance as standard would be necessary. 



In this way, by merely more precise definition, the simple, old terms 

 — crozvn density, croiun area., crozvn cover — ^can be retained and the 

 introduction of new terms avoided. 



Frothingham: 



Dr. Fernow designates three conditions : 



1. Density of individual crown: term, crown density. 



2. Area shaded by crowns : term, crown area. 



3. Total shading efficiency: term, crown cover. 



1 and 2 are the two.components of 3. In other words, it is a factor- 

 ing based on shading only. 



Silviculturally there are two important aspects of crown cover: 

 (1) interception of light, with respect to subordinate growth or forest 

 floor conditions, and (2) mechanical and other interference between 

 crowns in the crown cover without reference to subordinate growth. 

 With respect to the first, the term "shade density," a resultant of the 



