LITTER PRODUCTION I N FORESTS OF THE WORLD
143
carefully plucked and trimmed along with the same number of immediately adjacent green needles, and a dry weight loss of only 13% was
associated with browning. However, these brown needles were not quike
ready to fall, for they required a distinct tug with forceps to pluck them.
It was also apparent in this case that many needles remained long after
abscission upon the branches beneath, where they had become trapped
when falling. Presumably considerable weight loss might take place
before such needles reached a litter collector.
No data could be found for dry weight changes associated with
abscission of Warm Temperate or Equatorial tree leaves. However, in
1962, leaflets were sampled from a small leguminous tree, Tamarindus
indica, growing in the greenhouse of the Botany Department at the
University of Toronto. This tree has compound leaves with from
twenty to twenty-six opposite leaflets which yellow and drop off
separately. Collections were made of leaflet pairs in which one leaflet
was yellow, possessed a well-formed abscission layer, and dropped when
lightly touched; while the opposite leaflet was green, healthy and fimly
attached. Leaflets were washed with detergent to remove dust and other
contaminants, and oven-dried at 80°C for 12h. The results of four
leaflet collections from 2 March to 27 April showed the weight of yellow
leaflets to vary from 77 to 84% of that of green leaflets, with a mean
value of 81%. There was a slight tendency for the relative weight of
the yellow leaflets to decrease as the season advanced and solar radiation
and greenhouse temperature increased. On average, the Tamarindzls
leaves appeared to lose nearly one-fifth of their dry matter before falling.
In another test on 23 May 1963, leaves were collected from a Ficus
elastica tree growing in the greenhouse of the Botany Department at
the University of Minnesota. A very few of the leaves were yellow, and
fell when touched. Ten of these were collected along with immediately
adjacent green and healthy leaves of closely similar size. Four 21 mm
leaf discs were cut with a cork borer at random (but excluding the
midrib) from each pair of washed leaves. The green and yellow leaves of
each adjacent pair were superimposed so that disc locations would be
the same, and two discs were cut with the green leaf on top, and two
with the yellow leaf on top. Discs were then oven-dried a t 80' C overnight. The weight of the yellow discs was 81% of the weight of the green
discs, indicating (as in the case of Tamarindus) that Ficus leaves lose
nearly one-fifth of their dry matter just prior to abscission. It is interesting that results are identical for two leaves of such very different type,
the leguminous leaves being small and rather delicate, the fig leaves
large, leathqry and with a waxy surface.
143
carefully plucked and trimmed along with the same number of immediately adjacent green needles, and a dry weight loss of only 13% was
associated with browning. However, these brown needles were not quike
ready to fall, for they required a distinct tug with forceps to pluck them.
It was also apparent in this case that many needles remained long after
abscission upon the branches beneath, where they had become trapped
when falling. Presumably considerable weight loss might take place
before such needles reached a litter collector.
No data could be found for dry weight changes associated with
abscission of Warm Temperate or Equatorial tree leaves. However, in
1962, leaflets were sampled from a small leguminous tree, Tamarindus
indica, growing in the greenhouse of the Botany Department at the
University of Toronto. This tree has compound leaves with from
twenty to twenty-six opposite leaflets which yellow and drop off
separately. Collections were made of leaflet pairs in which one leaflet
was yellow, possessed a well-formed abscission layer, and dropped when
lightly touched; while the opposite leaflet was green, healthy and fimly
attached. Leaflets were washed with detergent to remove dust and other
contaminants, and oven-dried at 80°C for 12h. The results of four
leaflet collections from 2 March to 27 April showed the weight of yellow
leaflets to vary from 77 to 84% of that of green leaflets, with a mean
value of 81%. There was a slight tendency for the relative weight of
the yellow leaflets to decrease as the season advanced and solar radiation
and greenhouse temperature increased. On average, the Tamarindzls
leaves appeared to lose nearly one-fifth of their dry matter before falling.
In another test on 23 May 1963, leaves were collected from a Ficus
elastica tree growing in the greenhouse of the Botany Department at
the University of Minnesota. A very few of the leaves were yellow, and
fell when touched. Ten of these were collected along with immediately
adjacent green and healthy leaves of closely similar size. Four 21 mm
leaf discs were cut with a cork borer at random (but excluding the
midrib) from each pair of washed leaves. The green and yellow leaves of
each adjacent pair were superimposed so that disc locations would be
the same, and two discs were cut with the green leaf on top, and two
with the yellow leaf on top. Discs were then oven-dried a t 80' C overnight. The weight of the yellow discs was 81% of the weight of the green
discs, indicating (as in the case of Tamarindus) that Ficus leaves lose
nearly one-fifth of their dry matter just prior to abscission. It is interesting that results are identical for two leaves of such very different type,
the leguminous leaves being small and rather delicate, the fig leaves
large, leathqry and with a waxy surface.