Plant Communities of the World 271 



A number of conifer forests place themselves in the Lauri- 

 silvae on account of their physiognomy and distribution, and 

 apparently their ecology, which unfortunately is litde known. 

 The inner constitution of this systematic group does not allow 

 a real broad leaf, such as that of the dicotyledons, but they do 

 what they can in differentiating from the needle type. Scale-like 

 spreading and tile-like covering of the mass of closely knitted 

 leaves make something similar to a large broad leaf, glabrous 

 with a certain dim gloss, and at right angles to the incident light. 

 Thuja gigantea and Tsuga heterophylla have such forms. The 

 same result is reached by the broadening of needles and the 

 placing of one near another like a mosaic to make up big leaves, 

 as in Sequoia sempervirens. An ecologic anatomical research 

 concerning these forests is highly desirable; here they have only 

 been placed by analogy; because in distribution and habitat they 

 are similar to the well-known dicotyl laurel woods, it is assumed 

 that they need a similar climate. Such predictions have proved 

 right in the past (e.g., concerning heaths) ; may future studies 

 prove this one right also. Examples of these forests are found in 

 the northwestern United States, in the Coast Range and the 

 western Cascades with their mild winter (Seatde, mean January 

 temperature, +4.3°), cool summer (mean, July, 17.7°), small 

 difiFerence (13.4°), great quantity of fog (only 25 to 40 per cent 

 of the possible sunshine), and grizzly "Scotch" rain. A dense 

 canopy of giants with elegantly hanging branches makes a 

 wonderful impression. The hemlock, Tsuga heterophylla, with 

 a mosaic of parted needles and a sideways swing of branches, 

 gathers all possible light in the dim, dusky wood. Still broader 

 in foliage is the scale-leaved Thuja gigantea. In the Cascades, 

 fire has not rarely destroyed these associations and a Douglas 

 fir forest has sprung up as fire succession. The laurel leaf also 



