132 GERMINATION [CH. 



The plumule either pushes out from the same end of 

 the caryopsis as the root (e.g. Wheat, Rye) or drives its 

 way between the coats to the opposite end (e.g. Barley) 

 and appears as a pointed cylinder of rolled leaves (the 

 " spear ") the outermost of which is sheath only, no lamina 

 being developed. As Darwin showed, the pointed apex of 

 such a plumule is hardened, facilitating the piercing of the 

 soil above, and when the blade attains the open air it 

 performs spiral movements during growth, indicating that 

 similar attempts to rock from side to side have aided the 

 plumule in forcing its way through the soil. It has also 

 been shown that the apices of roots and plumules are 

 sensitive to differences of temperature, of light-intensity, 

 moisture and contact, all of which aid the seedling in 

 establishing its position in the soil and in liberating the 

 " spear.'' For particulars the student should read Darwin's 

 Power of Movement in Plants. 



With regard to the established seedlings of grasses, 

 many interesting details of structure are to be found in 

 them. I have not sufficient material to draw up a 

 diagnostic arrangement of grass-seedlings, but it is 

 evident that such could be done. It may be useful to 

 illustrate this by the following tabular view of the 

 characters of the larger seedlings of our common cereals, 

 in part adapted from Vesque and Percival ; though I find 

 that some variations may occur, especially in the develop- 

 ment of the auricles. 



