STRUCTURE AND GERMINATION OF SEEDS 33 



way upwards and uninjured through the soil. Examine the 

 grain of an older seedling (Fig. 12, 5) and note the changes 

 that have occurred. It is no longer a firm, solid mass, but 

 has become wrinkled ; and 

 when squeezed, readily col- 

 lapses, ejecting a milky- 

 looking fluid. 



As the green foliage-leaves 

 grow they push their way 

 out of the colourless sheath 

 (Fig. 12, sh) and unroll. 

 Soon a drop of water appears 

 on the tip of each leaf. 

 Where has this come from ? 

 Considering the conditions 

 under which the seedlings 

 have been grown, do you 

 think they are drops of 

 dew ? As the drops dry off, 

 note that a whitish deposit 

 is left. Is such a deposit 

 left when dew-drops evapo- 

 rate ? Note that such drops 

 occur freely when the seed- 

 lings are well supplied with 

 water. The root-hairs and 

 young roots absorb more 

 than the plant is able to 

 use, and the excess exudes 

 from pores at the leaf-tips. 



Fig. 14. Vertical Section of 

 Maize Grain. a.r, adventitious 

 root ; e, endosperm ; ep, epi- 

 thelium of the scutellum ; PI, 

 plumule ; ra, radicle ; r.c, root- 

 collar ; sc, scutellum ; st, stigma. 



This water contains mineral 



salts in solution, and when the exuded drops evaporate, 



the salts remain as a powder on the leaf-tips. 



Grains of Maize (Fig. 12, 6 and Fig. 14) and Oat should 

 be treated in the same way as the Wheat, and their parts 



1296 



