1 22 The Plant World. 



than the primary root, and often when it has reached its max- 

 imum length the root has not elongated more than one or two 

 centimeters. (Pg. 1-5.) 



Following the rapid gro\\ th of the cotyledonary petiole, 

 the primary root begins its period of elongation. Its growth 

 is also rapid at first but after a length of six or eight centimeters 

 has been reached, jnoceeds much more slowly and the increase 

 in diameter V)egins. This growth in length and diameter pro- 

 duces a flesh V structure ten centimeters or more in length and 

 with a maximum diameter of about one centimeter before the 

 phnuulc begins to groAv. There is very little woody tissue in 

 the root, but it consists principally of ])arenchymatous cells 

 richh filled with starch. The outer layer of cells 



becomes brown and corky and more or less deeply fissured 

 (figs. 7- 8.) The starch from the acorn is largely transported 

 down into this subterranean structure and stored within its 

 cells. Later the root increases in diameter by the addition of 

 woody cells and the plumule, which has been carried down 

 by the elongated petiole and has remained dormant, elongates 

 to form the stem. The stored starch is used up in the subse- 

 quent growth. In seedlings one or two years old, little starch 

 is to be found in this original storage tissue. The emptv par- 

 ench)matous cells form the jiith of the now gieatly enlarged 

 primary root. 



The plumule does not begin to develop until after the pri- 

 mary root has about reached the maximum size which 

 it ordinarilv attains before the woodv thickening begins. It 

 now begins to grow and in so doing separates the petiole into 

 two parts near the point of attachment to the rudimentary 

 hyi)ocotyl, and escapes through the opening. It appears 

 usually about six weeks from the time germination be- 

 gins, and doubtless under less favf)rahle conditions might be 

 delayed much longer. 



The young stem is so situated that it must attain a length 

 of six or eight centimeters before it reaches the surface of the 

 ground. The first leaves to develop are scale-like and nu mber 

 eight or nine. The first green leaves are much more notched 

 and serrate than is characteristic of the adult leaves of the 

 species. (figs. 9-lo.) 



