200 Maine Agricultural Experiment Station. 1920. 



The few references to be found in the literature do not 

 indicate which part of the embryo breaks through the pericarp. 

 If the embryonic region of a naked caryopsis of Alopecurus or 

 Arrhenatherum be examined with a low power lens at the first 

 stage of germination, it will be noticed that under the pressure 

 of the extending coleorhiza a small aperture is formed above 

 the hilum in which the tip of the coleorhiza appears. This aper- 

 ture soon gives rise to a slit which tends upwards, usually in the 

 middle plane of the embryo, and grows wider being extended by 

 the growing coleoptile up to the inner edge of the scutellum. 

 On removing the germinating embryo from the caryopsis a more 

 or less elliptical opening will be seen with the separated edges of 

 the pericarp projecting over it. Thus the rupture of the pericarp 

 takes place usually in a definite direction and, as a rule, is effect- 

 ed by the extending coleorhiza. During this process no loss of 

 tissues occurs. This is worthy of being mentioned since one 

 might be inclined to assume in connection with this process the 

 operation of chemical agencies that would loosen and absorb the 

 tissue elements. 



2. THE PENETRATION OF THE COLEORHIZA THROUGH THE 



LEMMA. 



After breaking through the tissues of the pericarp the 

 coleorhiza encounters the basal wall of the fertile glume or 

 lemma. The basal region of the lemma presents a detail of special 

 importance in connection with the breaking through of the cole- 

 orhiza. At its base the lemma of the grass-fruits forms a semi- 

 globular, disk-like or obtuse-conical callus which is separated 

 from the main body of the lemma by a transverse furrow, and 

 which is connected with the rachilla by means of a joint. In 

 this region a marked differentiation of tissues occurs. Before 

 describing the anatomical details of this region it is advisable 

 first to briefly discuss the tissue elements of the lemma. 



The lemma is composed of the outer and inner epidermis 

 and of the mesophyll enclosed by them. The elements of the 

 outer epidermis which forms the most powerful part of the 

 lemma in most grasses, are distinguished by their wavy longi- 

 tudinal walls whose indentations are most pronounced in the 

 middle section of the lemma. Here, as will be seen in Fig. 33 



