` 
LLOYD: GROWTH OF PROTOPLASM IN POLLEN TUBES 85 
overtake them. At certain concentrations below ca. N/640, the 
rates are lower than those for pure water, but much more markedly 
so for acids than for alkalis. 
2. The swelling rates and total swelling in acids is greater than 
in alkalis. 
3. The swelling rates and total swelling is greater in some 
organic acids (citric, malic) than in inorganic acids. 
Acetic and tartaric acids appear to be excepted. Malic acid 
has a far-reaching effect on gelatin in causing it to fragment at 
N/160 and above after one to two hours. This fact, together with 
the lower swelling rates at the higher concentrations, suggests 
that at these there is a coagulation effect which sets in to repress 
swelling. 
It thus appears that in trying to establish any analogy between 
gelatin (or other emulsoid) and protoplasm, the concentrations of 
the reagents to which they are subjected must be considered. For 
example, during the increase or decrease of acidity which may take 
place in the living tissues, the swelling effects may be alternately 
repressed and increased, aside from alterations in the relative 
composition of the body fluids due to change in salt, protein, or 
other content, such as MacDougal has indicated.* 
The determination of growth rates and accompanying phe- 
nomena in pollen tubes confirms the expectation that their pro- 
toplasm behaves toward the above reagents in many important 
respects as does gelatin rather than аваг. The method employed 
consists in sowing pollen of Phaseolus odoratus in hanging drops of 
the various reagents at different concentrations, associated with 
cane sugar in constant concentration, it having been foundt that 
the rate of growth of pollen tubes is inversely as the concentration 
of cane sugar, the maximum accomplished growth occurring in ca. 
20 per cent solution. It has been shown that this is explainable 
on the assumption that imbibition by the protoplasm rather than 
osmotic pressure is the dominant growth factor. In weaker solu- 
tions of cane sugar the pollen tubes burst, the lower the concen- 
* MacDougal, D. T. Science II. 46: 269. 14S 1917. 
T The contrary has been found to hold for complex tissues such as cactus stems 
by MacDougal and Spoehr. Proc. Amer. Phil. Soc. 56: 2 "e 1917 (and other al- 
ready cited papers). 
+ Lloyd, Е. E. Carnegie Inst. Wash. Апп. Rep. for 1916. 
