Germination of Grass-Fruits. 207 



lemma being separated from the strongly thickened, silicified 

 cells of the base. 



While these conditions are typical of Lolium, Festuca, Ar- 

 rhenathermn, etc. it occasionally occurs with other grasses that 

 the cells of the epidermis are rent by the coleorhiza. 



The formation of the longitudinal slits is facilitated by the 

 absence of the transverse. processes of the walls and the lack of 

 silicious cells at the base of the lemma. In yielding to the pressure 

 of the coleorhiza in the longitudinal direction the cells of the 

 epidermis and prosenchyma are pushed apart, the former remain- 

 ing usually, the later as a rule, intact. (Fig. 34). These slits very 

 often run along the fibrovascular bundles, where the thin-walled 

 parenchyma occurs in several layers. 



It should be added that the tracheal tissues are broken 

 through transversely and separated from the base of the lemma. 



Abnormal Germination of Grass-Fruits. 



Under normal conditions of germination the coleorhiza or 

 the radicle appear first, and, as a rule, at the base of the lemma. 

 At the beginning of this investigation several cases were observed 

 of hulled grass-fruits developing first the coleoptile while nothing 

 was to be seen at first of the radicle. A study of these cases 

 brought out the fact that a majority of hulled grass-fruits show 

 this type of germination which involves no physiological disturb- 

 ance, but is the result of external factors, like mechanical resist- 

 ance to and retardation of growth. The common feature of these 

 abnormal cases is that the radicle does not break through at the 

 base of the lemma. The different modes of abnormal germination 

 have arbitrarily been arranged here in two groups. 



Type A. The radicle appears either at the tip of the glumes 

 or in the opening between the lemma and palet, below the tip of 

 the lemma. The coleoptile appears, as a rule, outside the glumes 

 sometime before the radicle emerges. 



The following reasons account for the coleoptile appearing 

 ahead of the radicle. The radicle growing first downwards, then 

 bending at the base upwards covers in all cases a longer distance 

 than the upwards growing coleoptile. In many cases the lemma 

 is bent from the caryopsis thus exposing the coleoptile. Further, 

 the caryopsis may be lifted by the pressure of the radicle ; this 



