BULLETIN 294 



NORMAL AND ABNORMAL GERMINATION OF 

 GRASS—FRUITS.* 



BY 



Jacob Zinn. 

 SUMMARY 



The present paper is an account of the processes that take 

 place at the time of emergence of the radicle of hulled grass- 

 fruits from the surrounding tissues. 



The penetration of the germinating embryo through the 

 tissues of the adhering pericarp is a purely mechanical process*. 

 Under the pressure of the extending embryo a section of the 

 tissues yields at a certain point and usually in a certain direc- 

 tion. 



At normal germination the coleorhiza breaks through the 

 base of the fertile glume within a zone whose mechanical resis- 

 tance is greatly lessened by the marked reduction and differen- 

 tiation of the epidermal and hypodermal mechanical cells. The 

 prosenchymatous tissue yields along lines of contact of the long 

 sclerenchymatous cells and the short basal elements of the 

 glume. Likewise, the epidermis is ruptured in a region where 

 cells marked by different morphological forms and physical 

 structure meet. In both cases the cells are pushed apart, the 

 sclerenchymatous cells remaining, as a rule, intact while the 

 epidermal cells mostly escape injury. The tracheal elements of 

 the fibro-vascular bundles have been invariably found to be 

 broken through. 



The abnormal germination of hulled grass-fruits is caused 

 by external mechanical factors prevailing in artificial germina- 

 tion media which operate so as to thwart and eliminate the 



*This is an abstract from a paper by the author having the title: 

 "Ein Beitrag zur Keimungsgeschichte der bespelzten Grassfruchte," and 

 published in "Mitteilungen der landw. Lehrkanzeln der k. k. Hochschule 

 fur Bodenkultur," Vol. II, pp. 675-712, 8 pi. 24 figs. Wien, 1914. 



