IN SPRUCES AND FIRS. 5 
case in the flat-leaved spruces, the leaves arising from the shoot 
on either side of the median plane twist more or less on their 
bases according to their positions on the axis, the amount through 
which each twists being equal to the angular divergence of its 
point of insertion from that of a leaf inserted in the median 
plane in which no twisting takes place; but, contrary to what 
takes place in the case of the spruces, the twisting here com- 
mences in the leaves adjacent to those in the median plane upon 
the under side of the shoot and increases as successive leaves 
are passed through in an upward direction. These leaves also 
move upwards or downwards, according to their positions 
on the axis, by a swing movement at the base, into more or less 
horizontal positions, as in the case of the leaves corresponding 
with them in position on the horizontal shoots of the flat-leaved 
spruces, and they also move outwards into positions more or less 
divergent in direction from that of the shoot ; but this movement, 
unlike that which occurs in similarly situated leaves in the flat- 
leaved spruces, varies in different species of flat-leaved silver firs. 
In species such as Adzes grandis and A. Lowzana all the leaves 
on the horizontal shoots move outwards into positions nearly at 
right angles to the direction of the axis, so that a “ pectinate ” 
arrangement is produced; but in other species such as 4. 
amabilis and A. Nordmanntana the leaves on the upper sides of 
the horizontal shoots assume a disposition having a somewhat 
superficial resemblance to that of the leaves of the flat-leaved 
spruces, inasmuch as the uppermost leaves, in addition to twisting 
on their bases, often bend forward, so that they lie almost parallel 
in direction with the shoot, while those adjacent to them on 
either side move outwards into positions more or less divergent 
in direction from that of the axis, the divergence increasing as 
successive leaves are passed through in a downward direction to, 
in some instances, nearly a right arigle in those adjacent to the 
leaves in the median plane upon the under side of it.} 
1 These species are taken as representing perhaps the two extremes of leaf-arrange- 
ment in the flat-leaved silver firs—A. grandis, Lindl., and A. Lowiana, Murray, on 
the one hand being very pronouncedly “‘ pectinate,” while 4. amadilis, Forbes, and 
A. Nordmanniana, Spach, are more or less what may be termed ‘‘spruce-like.” 
Between these exttemes lie a number of species which are more or less intermediate, 
such as A. pectinata, DC., A. er et Mill., A. sibirica, Ledeb.,A. Vettchit, Lindl., 
and others, 
