160 Physloloffical Pre-detennination 



infected control seed. Heads of maize picked before maturity were 

 placed in a damp atmosphere under bell jars at the laboratory tempera- 

 ture. After an interval of 15 days it was found that the seeds, which 

 had germinated, corresponded with the infected areas on the head as 

 indicated by the presence of fungal mycelium. Maze suggested that 

 these organisms in some way destroyed the aldehyde, since the seeds 

 which had germinated after inoculation were found to contain no 

 aldehyde, whereas in a control head which was not inoculated a con- 

 centration of roughly -^^^^ aldehyde was found in the cell-sap (cf. also 

 Maze (18)). 



Lastly, Maze rules out direct oxidation processes as being respon- 

 sible for the effect produced by desiccation. He dried some immature 

 maize seeds in a vacuum and others in an atmosphere of COg and found 

 that in both cases the effect produced was similar to that produced by 

 drying the seeds in air. 



Babcock(2), however, believes that the characteristic effect of drying 

 in rendering immature seeds capable of immediate germination is to 

 be traced to an increase in direct " respiration," since the same effect 

 can be produced without drying by treating the seeds with hydrogen 

 peroxide. He suggests that the change brought about in the seed by 

 increased respiration is the liberation of diastatic enzymes, which, 

 according to Babcock, are normally absent from immature seeds. 



His experimental data are meagre. There seems to be no criterion 

 to distinguish cause from effect. 



In a recent communication (Kidd(i5)) it has been shown that the 

 testa may play an important rdle with regard to the germination of 

 immature or unripe seeds. In the case of Brassica alba and Pisiuii 

 sativum it was found that the removal of the testa not only accelerated 

 germination in the same way as drying, but also increased the germina- 

 tion percentage of unripe seeds as is shown in the following Table III. 

 It is clear that the rest-period observed when attempts are made to 

 germinate green immature seeds may be largely attributed to the 

 presence of the living testa which, in the author's opinion, functions 

 by limiting gaseous exchange to the embryo^. 



Although the point has not been fully investigated, the results so 

 far obtained tend to show that there is no inherent rest-period in the 

 developing embryo itself. Recent observations of Duggar(6) may be 

 mentioned in this connection. 



^ The testa dies during the process of drying and its iluuaoter as a nicinbiani> is 

 thereby completely changed. 



