210 PHYSIOLOGY [Bot. Absts., Vol. IV, 



mino-acids,' glycerine; of colloids, gelatin, albumens, glue, gums. These are really states, 

 and the power to change from the one to the other seems the very essence of cell life. —Col- 

 loids are generally divided into different phases depending on their more liquid or jelly-like 

 condition. Hydrosols are pseudo-solutions, hydrogels are either emulsions or coagulated, or 

 precipitated. — The particles of colloids do not enter into real solutions, but usually exist as 

 suspensions which can be seen with the ultra-microscope. But they are also known to be in 

 suspension and not in solution from the facts that boiling and freezing points of these fluids are 

 not much changed and no osmotic pressure is developed. A few colloids do show these 

 effects and these are soluble. — The foam structure, granular structure, networks, spindle fibres, 

 chromosomes, and the like originate by the more or less solid condition of the multimolecules 

 and large molecular complexes. — Colloidal gels are reversible and non-reversible, gelatin being 

 an example of the former and egg albumen of the latter. — Colloidal particles behave as a single 

 particle in bearing electrical charges, the acid generally being negative and the alkaline 

 positive. Hardy has made an extensive study of the electrical properties of colloids. — The 

 irritability of the human organism is largely due to the state of the colloids in the nervous 

 system, the gel condition causing irritability. — "Only by understanding the reaction of the 

 three substances entering into living combinations, namely, water, crystalloids, and col- 

 loids can we hope to comprehend such living processes as metabolism, growth, irritability, 

 and the like; and in order to understand life or the life process the biologist must give his 

 moments to the study of colloids. — L. Pace. 



1397. Stbckbeck, D. Walter. The comparative histology and irritability of sensitive 

 plants. Contrib. Bot. Lab. Univ. Pennsylvania 4: 185-230. PI. 58-65. 1919.— The investi- 

 gator notes that the sensitive plants are most common in tropical countries and that the most 

 widespread irritable response is the nyctitropic, probably induced by rapid changes in tem- 

 perature, transpiration, and radiation in transition from day to night. Paraheliotropic 

 responses followed with responses to light and mechanical stimuli in sequence. The compara- 

 tive histology of the sensitive structures is given with emphasis on the various kinds of crys- 

 tals of calcium oxalate restricted to the endodermis with the membranes surrounding the 

 crystals arranged to form continuous protoplasmic connections throughout the endodermal 

 region as the special conducting lines for the passage of stimuli. It was found that with transi- 

 tion from the less sensitive to the more sensitive species the cells of the pulvini contain, in 

 increasing amount and complexity, aggregation bodies resembling those previously described 

 by Darwin, and others, as associated with irritocontractile centers, and which change under 

 stimulation. All irrito-contractile changes seem to be due to changes first in the protoplasmic 

 sac surrounding each aggregation body, next in the aggregation body itself, finally in the 

 amount of liquid these absorb or give off. The complex hairs of the plant act as delicate 

 receptors of the stimuli. — John W. Harshberger. 



1398. Tolman, Richard C, and Russell S. Bracewell. The molecular mechanism 

 of colloidal behavior. II. The swelling of fibrin in alkalies. Jour. Amer. Chem. Soc. 41: 1503- 

 1510. 1919. — "Tolman and Steam have studied the swelling of fibrin in acid solutions, and 

 correlated the swelling with the amount of acid absorbed from the solution." They think 

 fibrin covered with water is a fibrous, spongelike structure with many pores full of water. 

 The addition of the acid is followed by the adsorption of hydrogen ions to form a double 

 layer on the surface of these pockets with an increase in size owing to electrostatic repulsion. 

 The addition of a neutral salt or the further addition of acid is followed by a decrease in 

 swelling because of the neutralization of the original electrostatic repulsion. The addition 

 of a neutral salt leads to further adsorption of acid owing to the fact that the neutralization of 

 the electrostatic forces makes it easier for further hydrogen ions to attach themselves to the 

 walls of the pockets. The effect of strong alkalies is similar to the above. — J. M. Brannon. 



DIFFUSION, PERMEABILITY 



1399. Anonymous. Honey. Newest theories concerning the function of the nectary in 

 flowers. Sci. Amer. Supplem. 88: 22-23. 1919.— See Bot. Absts. 4, Entry 977. 



