1919] AGRICULTURAL BOTANY. 519 



The response of Pilobolus to light, R. Pars (Ann. Bot, [London}, -li 



(1918), Ao. 126, pp. 177-M5, fi</s. 4).— Tin- author gives an account Of a Berlefl 

 of studios attempting to supply in work with Pilobolus the, alleged lack <>f ac- 

 curate determination of the quantity and quality of the light employed in such 

 work, so as to ascertain the relation between light and hellotroplc response. 



Pilobolus responds to light from all portions of the visible spectrum, the 

 presentation time gradually decreasing from red to violet and varying Inversely 

 as the square root of wave frequency bul not directly as the value of the energy 

 from different portions of the spectrum. The product of the square root of wave 

 frequency by the presentation time decreases as does energy value within the 

 spectrum, and it is approximately constant for a given source of light The re- 

 lation of special energy to the presentation time may he expressed approxi- 

 mately by the Weber-Feel iner or the Trondle formula if wave frequency be 

 made a function of the constant. 



The structure of the integumentary system of the barley grain in rela- 

 tion to localized water absorption and semipermeability, B. J. Collins [Ann. 

 lint. [London], 32 (1918), No. 127, pp. 881-^1 l h figs. U,).— It is claimed that the 

 general surface of the barley grain admits only a small part of the water ab- 

 sorbed by the seed. Special areas readily admitting water occur in the germl- 

 nal portion of the grain, and here is thought to be located the structure con- 

 cerned in the selective permeability expressed In comparatively free admission 

 of water along with practical exclusion of mineral acids and most salts. Such 

 solutes as acetic acid and iodin, recorded as passing freely into the grain, 

 really pass through the restricted area near the germinal portion. Nitric acid 

 enters as the result of selective action, neither destroying the enveloping mem- 

 brane nor impairing the etliciency of the selective structure. Perfect Imper- 

 meability to any solute was not observed. The initial concentrating effect of 

 barley upon dilute sulphuric acid gradually decreases until the acid is below 

 its initial concentration. Arrest of penetration of silver nitrate and of sodium 

 chlorld occurs at the outer cutlcularized wall of the tegmen. This membrane 

 behaves as does ordinary cuticle in regard to penetration by water and solutes. 



The initial uptake of water supplies the need of the embryo, the grain cover- 

 ings insuring sufficient conduction of water to where It can be readily absorbed 

 by the embryo. The subsequent distribution of liquid In the endosperm is pre- 

 cisely the path of enzym disintegration in the endosperm during the germination 

 of the embryo. It is suggested that the uptake and distribution of water in 

 germination prepares for and perhaps accomplishes the distribution of euzyms 

 which are active In the solution of reserves. 



The laticiferous system of Hevea brasiliensis and its protective function, 

 A. Shabplbs {Ann. Bot. [London], 32 (1918), No. 126, pp. 247-&51).— In order 

 to settle the question of whether scraping the bark of Hevea with the view 

 of stimulating increased flow of latex renders the trees more susceptible to 

 insect and fungus attack, the author experimented with 30 well-grown trees 

 five years old. 



The results are said to show that the removal of the outer corky layers in- 

 creases susceptibility to insect and fungus attack, particularly If the green 

 cork cambium is removed or broken. This may be connected with the con- 

 tinued soaking of the tissues and the slowing up of the normal activities dur- 

 ing a period of wet weather and the consequent lowering of resistance. It is 

 stated that scraping away the scaly bark on old trees to insure a clean yield 

 of latex can be done without injury if care is employed. The question as to 

 whether latex is a secondary and waste, or primary and necessary, product 

 Is regarded as not yet settled. 



