WRIGHT: FOLIAR PERIODICITY 
therefore only obtain new tissues by casting off the old 
members and producing entirely new leaves. It is obvious 
however that the same change can be obtained by a monthly 
fall and production of leaf. With respect to the possible 
necessity of throwing off the useless ehemical ingredients 
when they have accumulated beyond the desirable degree of 
concentration, it may be stated that the yellow leaves of Eryth- 
rma indica as they fall from the tree contain 7 per cent, of 
lime. Nevertheless, it is erroneous to suppose that trees 
when throwing off their old yellow leaves are casting off 
members containing hardly any valuable food ingredients. 
Mr. Bruce analyzed several of the yellow fallen leaves of the 
common dadap (Erythrina indica) and found that they 
contained no less than 1*4 per cent, of nitrogen, 0 56 per cent, 
of potash, and Oil per cent, of phosphoric acid. These ingre- 
77 77 aTOUaWe in large qaantitie8 in Ce y>° n soils and 
the loss to the plant, temporary though in some cases itmav 
be 7 one winch is not always seriously considered. 
The mam advantages are, however, probably to be asso- 
77m 777 t mge “ f “ ctional ° £ P^a of the 
exposed to r 7 ” eCCB8ar> ' that “>« ‘^es bo continually 
exposed to light m order to snccessfnlly carry on the 
various fnnctions of the plant. Experiments^, various 
£The TLTr 4 that Wt ™ light is sn PP lied intermittently 
to the aseimilatory organs the various functions are carried 
AaitL sIlr'Ly bl^d^ ^ C ° ntmaon8l y eopplied. 
leaves of ^ 
number of months each year Bv '7* ^ * Varying 
tently to the stuTTs of l^L^T777* ‘7™“' 
varying activity of many functC ** 
t. 
The piants Obtain TperioHr^fr^ 
of *■ 
