24 BOTANY 



sperm swells and the flat cotyledons which remain in 

 contact with it begin to absorb the contents of its 

 cells. The face of the endosperm becomes very slimy 

 or mucilaginous and it continues to swell for some 

 days, ultimately cracking and being loosely attached 

 to the absorbing cotyledons. The hypocotyl grows up 

 in the form of a loop and drags the cotyledons out of 

 the soil with the endosperm clinging to them. They 

 very quickly change colour, becoming yellow and ulti- 

 mately green, and as the last traces of the endosperm 

 are used up they grow out laterally and take on the 

 appearance and the function of foliage leaves. 



CHAPTER III 



THE FORMATION OF THE ROOT SYSTEM 



THE seeds just described are very useful for observing 

 also the growth and development of the seedling. Even 

 better material for this purpose is supplied by the seeds 

 of the common cress. If several of these seeds are 

 soaked in water and then scattered over the inside of a 

 damp flower pot they will germinate very freely if the 

 pot is kept moist and moderately warm, putting out 

 their roots in a few hours. As they will have been sown 

 quite indiscriminately, their positions will be irregular 

 and the young rootlets will emerge at first in very 

 different directions. If they are allowed to remain un- 

 disturbed as they elongate they invariably manage to- 

 direct their apices downwards, effecting sometimes 

 curious curvatures to do so. This strange uniformity 

 of behaviour suggests that the young seedling has a kind 

 of appreciation of its position or the direction of its 

 growth. We can test this suggestion by taking several 

 of them from the positions they have assumed and 

 placing them so that their roots are at different angles 



