262 



The fact that the pericarp is greatly modified at the tip of the 

 grain — the pedicle — into a very porous vascular tissue, introduces a 

 factor that greatly increases the difficulty in a study of the mem- 

 branes. At this point, however, the pericarp is reinforced within by a 

 compact remnant of the nucellus which, when perfect, effectively pre- 

 vents the oil from penetrating the grains. There can be no question but 

 that this is the usual point of ingress into those grains in which the 

 embryos are stained. The colored oil invariably makes its appearance 

 here and gradually passes up through the embryo. That the pedicle 

 itself is not only valueless for excluding the oil but that it is the source 

 of positive injury is shown in Table 6. The pedicles were carefully 

 broken off from these grains before immersing them in kerosene, and it 

 was found that a higher rate of germination resulted from grains so 

 treated. It is altogether likely that the spongy tissue of the pedicle, by 

 retaining rather large quantities of the kerosene, is responsible for a 

 decrease in germination when it is not removed. The oil remaining 

 in or on the grains seems to be absorbed and carried to the regions 

 of growth as soon as the growth processes are initiated. If the 

 amount is beyond a certain limit, injury is produced. 



The -effects of removing the pedicle and slightly puncturing the 

 membranes within it are shown in Table 8. The best place to puncture 

 the pericarp without injuring the embryo is near the distal end of the 

 coleoptile where, in the process of maturing, a small wrinkle is formed 

 in a rather large proportion of the grains. The membranes at this 

 point can readily be ruptured with a needle without the slightest in- 

 jury to the underlying parts. 



The effects of thus puncturing the coats (Table 7) are in a gen- 

 eral way comparable to those secured by puncturing the membranes 

 lying within the pedicle. In the latter case, however, the grains did 

 not show the injurious effects as c|uickly as in the former. In both 

 cases the colored oil penetrated the embryos in sufficient quantities to 

 be plainly visible in twenty-four hours. It is important to note that, 

 excepting a slight retardation, 100% of the grains in Table 8 con- 

 tinued to produce normal seedlings after immersion in kerosene for a 

 period of ten days. This shows that the presence of a limited amount 

 of oil in the embryo is not necessarily injurious. 



By soaking the grains in tepid water for ten minutes the entire 

 pericarp, including the pedicle, is very easily removed without in- 

 jury to the parts within. After thus removing it, the grains were 

 dried at room temperature for five days and then immersed in kero- 

 sene. The results (Table 9) correspond closely to those obtained in 

 the experiments with punctured membranes and show that a punctured 



