636 Harper. — Defoliation : its Effects ttpon the 
a second leafing due to an especially favourable autumn. But in this same 
tree a second crop of leaves did not always mean a double ring, especially 
in the lower parts of the trunk, for there autumn wood formation generally 
begins a little later than in the upper parts, Now after defoliation by the 
Sawfly larvae the larches sometimes put out fresh leaves towards the close 
of the summer, possibly after the formation of autumn wood has already 
begun. Spring wood is generally formed between the middle of April, 
when growth begins, and the end of June, after which month autumn wood 
is produced, until growth ceases about the end of August or beginning of 
September. 1 The defoliation of the larches, beginning in June, is usually 
over by the end of July, and a second crop of leaves may appear about the 
middle of August, i. e. before the end of the year’s growth. According to 
Strasburger’s view, these new leaves would stimulate the cambium to 
a renewed formation of spring wood outside the first few autumn tracheides, 
while the lateness of the season or scarcity of food might preclude a second 
development of autumn wood to finish off the ring. 
Another explanation of the abnormal formation of thin-walled cells at 
the outer limit of a ring may be put forward on the grounds of experiments 
by Lutz, who found that artificial defoliation and prevention of a second 
leafing led to the production of spring wood at a time of year when autumn 
wood was to be expected. 2 He supposes that the decreased transpiration 
of the defoliated branches had resulted in the tree filling with water, and 
that the presence of much water determines the formation of spring wood. 
This view, in opposition to that held by Strasburger and by Haberlandt, 
already mentioned, is supported by the fact that on wet ground Pinus 
sylvestris makes very poor autumn wood, 3 and it would seem to be 
applicable to those defoliated larches where a second leafing has not 
occurred or is only partial. 
To determine, if possible, how far altered conditions of nutrition or 
a second growth of leaves might affect the formation of autumn wood, 
certain larches were investigated in districts free from the Sawfly, but 
where the abnormal summer of 1911 had destroyed some of the shoots of 
that year, thus prematurely cutting short the normal elaboration of food 
materials. For instance, in some young Japanese Larches growing near 
Oxford, all the shoots of 1911 had been dried up at the tips, so that all the 
leaves of the following summer were of necessity those of spur shoots. 
When one of these trees was examined it was found that in the ring of 1911 
the zone of thick-walled autumn wood passed quite suddenly into a very 
narrow zone of thin-walled cells quite distinct from the spring wood of 
1912 by reason of smaller size and tangential flattening. This unthickened 
zone was found throughout the whole tree ; its cells seemed to have been 
1 Cp. Hartig ( 1 ). 2 Lutz, 1895. I am at present investigating this matter. 
3 Cp. Ramann and Bauer. 
