GERMINATION OF THE SEED l8l 



marked by a slight constriction or by the first side roots. 

 Students will tend to call the main root hypocotyl, and to 

 call only the side branches "roots," which must be corrected. 

 The structure of the root, including the tips and root hairs, is 

 very plainly seen through the glass, especially by use of a lens, 

 and should be well worked out. Full labelling, to bring out 

 the homologous parts, is very important. 



In facts of ecology, they will notice that root grows faster 

 than plumule (of course because absorption of moisture is a 

 first need), and that size of seed, position in which planted, 

 amount of moisture, all have something to do with the dif- 

 ferent rates of development of the same kinds of seeds, to 

 which some students will probably add a real difference in 

 their living matter, which is strictly true. We have here an 

 introduction to facts of individual variation, so important in 

 evolution. From some of each of the kinds in the boxes, the 

 young plumules should be pinched off, the results to be noted 

 the next week. 



It would be of interest also in this connection to study the 

 germination of Horse-chestnut, but practically it is very diffi- 

 cult to germinate. 



They will, of course, readily notice in Exercise 10 (7) that 

 the position taken by hypocotyl and plumule (or rather epi- 

 cotyl), in growth, bears no relation whatsoever to the position 

 of the seed, but that, regardless of this, all hypocotyls bearing 

 the roots grow down, and all plumules grow up. They should 

 then be led to ask what determines this up-and-down position 

 (that is, how does the young plant know which is up, and 

 which is down), whether darkness below, or the moisture, or 

 something else ; they may be encouraged to experiment upon 

 these, and then their minds will be in condition to appreciate 

 the results of Exercise 15. 



