ROOT- CAPS. 35 



have been grown in sandy soil ; grains of 

 sand will generally be found adhering in great 

 numbers to the region on which we now know 

 the root- hairs occur. Wash off 'this sand very 

 carefully, and, whilst the roots are suspended 

 in a tumbler of water, examine them also for 

 root-hairs. 



ROOT-CAPS. 



Examine the aerial roots of the screw- 

 pine and observe their root-caps; then look for 

 similar, but much smaller and more delicate 

 structures on other roots. Examine also roots 

 growing in water ; some water-plants have no 

 root-caps, but if the water- hyacinth (Eichor- 

 nia) can be obtained, its roots will be found 

 to show root-caps to perfection. These roots 

 should be examined whilst still in water. 

 Grow seedlings and cuttings in water and 

 examine their roots for root-caps. 



GROWTH IN THICKNESS. 



I. The youngest part of a root is always 

 the thinnest ; this is readily seen by observing 

 any of the seedlings already obtained. In most 

 of the plants which have only one cotyledon 

 the roots soon stop growing in thickness and 

 accordingly all the older roots are of a uniform 



