202 Maine Agricultural Experiment Station. 1920. 



mechanical resistance of the basal zone of the lemma. The tur- 

 gor increases with the growing activity of the coleorhiza and 

 reaches a point, when it equals the resistance of the lemma. If 

 the coleorhiza is now to effect the breaking through the lemma 

 it is essential that the caryopsis be properly anchored so as to 

 avoid its being pushed back or aside by the presence of the ex- 

 tending coleorhiza. Normally, the caryopsis at germination in 

 artificial media is prevented from receding by its firm cohesion 

 to the palet, and occasionally, to the lemma. The pressure of 

 the coleorhiza exerted against the base of the lemma finally over- 

 comes the resistance of the latter and a rupture of the tissus in 

 that region ensues. 



The macroscopic aspect of the rupture at the base of the 

 lemma varies somewhat with different grasses but with the same 

 species it always occurs in a definite manner. On examining the 

 germinating caryopsis of Lolium italicum or Festuca arundina- 

 cea just previous to the appearance of the tip of the coleorhiza, 

 it will be noticed that the primary fissure runs in a transverse 

 direction, generally along the basal furrow above the callus re- 

 ferred to above. Soon after, the pressure of the protruding 

 coleorhiza causes the tissues at the base of the lemma to split 

 forming longitudinal slits which extend upwards for some dis- 

 tance. The section of the lemma, severed from its base by the 

 coleorhiza, may either be bent off as a coherent piece (Lolium 

 italicum, Festuca arundinacea, Panicum miliaceum) or split into 

 more or less wide stripes (Arrhenatherum, Dactylis, Avena, 

 Holcus). The primary transverse fissure was never found to 

 extend beyond the marginal vascular bundle. 



While these conditions are typical of the majority of hulled 

 grass-fruits, the coleorhiza of certain grasses breaks through the 

 lemma in a manner somewhat different from the one just des- 

 cribed, and characterized by the longitudinal slit occurring in a 

 distinct region and direction. To this group belong grasses 

 whose caryopsis and glumes are flattened, the embryo facing the 

 strongly carinated, dorsal, fibrovascular bundle of the lemma, 

 e. g. Alopecurus pratensis, A. geniculatus and A. agrestis, 

 Phalaris arundinacea and canariensis, Oryza sativa and Bromus 

 Schraderi. Here the rupture of the lemma occurs along a line 

 of contact of the parenchyma and the median fibrovascular 

 bundle. With the exception of a few cases — in the glume of 



