82 EXPERLMENTAL PLANT PHYSIOLOGY 



fined to simple experiments dealing with causes and 

 methods of growtn, and the experiments should be 

 worked in conjunction with the morphological study of 

 the germination of the seed. 



For this reason it is sufficient here to trace briefly 

 the course of events in some individual case, say in the 

 germination of a broad-bean. 



When a broad-bean seed is planted in a pot of earth, 

 and kept damp and in a warm place, it very soon begins 

 to grow. First it absorbs some of the moisture and 

 consequently swells. This swelling produces so much 



Pressure on the coat, or testa, that a rupture is caused, 

 he testa bursts at its weakest point, that is, at the 

 point where there was already a small hole, the micro- 

 pyle. The first root, or radicle, whose tip was just 

 beneath the hole, protrudes through the ruptured coat 

 and grows down into the soil. Soon after this, the first 

 shoot, the plumule, bent like a hook and with its yellow 

 leaves all crowded together at the tip, pushes its way 

 through the soil up to the light and the air. 



The seed germinates because it has been supplied 

 with all the conditions necessary for its development. 



These conditions, which together make up its environ- 

 ment, may be examined separately in order to find out 

 which are essential to the growth of the seedhnij. 



A. Water as a Necessary Factor in Germination 



EXPEKIMEXT 50 



Aim. — To find out whether a seed will germinate 

 without water. 



Method. — Some bean seeds are planted in a pot of 

 well-dried soil, and others in a pot of damp soil. The 

 seeds in the damp soil are watered regularly- in the 

 usual way. 



Observations. — The seeds in the damp soil germinate. 

 Those in the dry soil do not. 



Inference. — A seed will not germinate without water. 



