194 BOTANICAL GAZETTE | MARCH 
treated in the same way December I, the average growth of the 
upper half in two days was 4.4™™"; of the lower, 9.1™™. Of thir- 
teen plants split 1™ into the root and placed in horizontal 
tubing, the average growth of the upper halves in two days was 
2.4™™, and of the lower halves, 4.4™™. Three plants were turned 
over; and after two more days the halves of two of them were 
equal, but in the other the difference had increased. 
It has now been shown for hypocotyls and epicotyls, hollow 
and solid stems, fixed at either end by imbedding in gypsum 
plaster or pinning with glass pins, or grown in glass tubes, that 
the rate of growth of an isolated half stem is greater, in general | 
perhaps twice as great, if it occupies the position of the inferior 
half of an uninjured prostrate stem, than if it is in the position 
of the superior half. As to the fact, the proof is surely sufficient. 
But so far no explanation has suggested itself, which was not 
more easily confuted than conceived. 
After looking in vain for a real reason, I turned to the 
mechanism of the growth, but have been unable ina consider- 
able number of experiments to detect any well marked or con- 
Stant difference in turgor between the halves. If the turgor 
of the growing region at a fixed distance below the insertion of the 
cotyledons is determined it will be found less in the upper half, 
but this is because the growing region is shortened. If the zone 
which is elongating most rapidly is tested in each case (this will 
be perhaps 2™™ nearer the base in the under half) there will be 
found almost no difference in the turgor. The results from test- 
ing a number of plants were very constant, and the following . 
_ May serve as an example. The halves had been horizontal for 
four days. Turgor is measured in percentage concentration of 
KNO, necessary to begin plasmolysis. 
Lupinus albus. 
U h if f 
Growth eee : a 
; Growing part Grown part Growing part Grown part 
Turgor a 4 3 4 3-5 
ee 8 3-3-5 4 3-3-5 
