Germination of Grass-Fruits. 201 



the wavy lines of the longitudinal cell-walls are transformed into 

 transverse processes, which with some grasses attain a length 

 equaling the width of the cell. These transverse processes of the 

 longitudinal walls fit into the corresponding indentations of the 

 adjoining cells thus establishing a mechanical resistance of this 

 system of tissues in the longitudinal direction. Embedded in 

 between the longitudinal walls of the adjoining cells are thick 

 silicious cells, one-celled and two-celled little hairs. These func- 

 tion as rivets, so to speak, establishing a connection of the cells 

 in the longitudinal direction and preventing a dislodging of the 

 epidermal cells in the transverse direction. The mechanical 

 firmness of this system of tissues is further enhanced by the 

 thickening and silicifying of the cells. The mesophyll beneath 

 the epidermis is differentiated into two layers : The prosenchyma 

 composed of specific mechanical cells and the parenchyma made 

 up by thin-walled cells carrying chlorophyll at their early stage 

 of growth. The prosenchyma is composed of elongated, very 

 thick, porous, spindle-shaped cells, (Fig. 35, C.) which owing to 

 their very marked growth in the longitudinal direction, inter- 

 lock with each other. (Fig. 35, A.). The lemma of the true 

 grasses contains usually 1-3 layers of these cells. The number 

 of layers of parenchymatous cells increases towards the vascular 

 bundles. As will be seen later this increase in parenchymatous 

 tissue around the vascular bundles and at the base of the lemma 

 is of importance in connection with the breaking through of the 

 coleorhiza. Beyond the marginal vascular bundles the cells of 

 the parenchyma become thick-walled, their lumen decreases as 

 well as their number until at the edge of the lemma they disap- 

 pear. The sclerenchymatous cells undergo a similar reduction 

 so that at the lower outer edge of the lemma the thick-walled 

 cells of both the outer and inner epidermis lie upon each other. 



The inner epidermis is composed of thin-walled, elongated, 

 colorless cells, possessing, when young, a very large lumen. 



The differences in thickness and tenacity of the lemmas of 

 different grasses is caused by the variation in the number of cell 

 layers and the degree of thickening of the elements of the outer 

 epidermis and the prosenchyma. 



Returning now to the processes occurring during the first 

 stages of germination, the coleorhiza, after breaking through the 

 pericarp, directs the energy of its turgescent cells against the 



