PERIOD OF EARLY GROWTH. 55 



GROWTH AND DEVELOPMKNT. 



lu a fruitful year, before the close of the season, witli the advent of spring, a dry and sunny 

 state of the atmosphere favoring the fall of the seed, the seedlings are ibund to come up abun- 

 dantly iu every opening of the forest where the rays of the sua strike the dry ground. The lower 

 (hypocotyledonary) parf of the axis of the plantlet is close to the ground, with eight to tea erect 

 colyledous from 1 to li inches in length, their tii)s inclosed iu the shell of the seed, with the long 

 wing persistent and borne banner-like at the top of tiie plantlet (PI. VII, a). The elongation 

 of the ascending axis proceeds slowly, growth iu length l)eing retarded until a certain thickness 

 h;us been attained, resembling in this respect the growth of the stem of endogenous trees. 



Upon examination of a seedling iu the latter part of April the cotyledons had disappeared 

 and the caulicle was found to be from one-eighth to one-fourth of an inch long, its length not 

 exceeding its diameter, hidden by a dense tuft of the needle-shaped primary leaves, which closely 

 invest the terminal bud. At this stage a few fascicles of secondary leaves are already showing 

 themselves, still inclosed in their slieaths. 



During the first three or four years its energy of growth is mainly expended upon the 

 development of its powerful root system (see PI. VII, e). Before the first spring season has 

 passed, tlie stout spindle-shaped taproot of the seedling is found to be over 3 inches iu length and 

 provided with several fine lateral lootlets, sometimes nearly as long as the main root. 



With the opening of June the primary leaves covering the axis are nearly all withered, only 

 a few remaining to the end of the season. With the development of the suppressed secondary 

 axes from which the foliage leaves proceed, the primary leaves are reduced to chafty fimbriate 

 bracts. Only few of these primary leaves retain the needle shaped form and green color, namely, 

 those from which no leaf-bearing brauchlets were developed. During the first season many of the 

 fascicles of the foliage leaves contain only two leaves, and sheaths inclosing only one leaf are 

 frequently observed. 



By the end of the first year the stem of the plantlet is rarely over three-fourths of -an inch iu 

 length, the main root having attained a length of from 8 to 10 inches. 



Having reached the end of the second year the taproot is found from li to 3 feet in length, the stem 

 scarcely 1^ inches long, with an increase of diameter hardly perceptil)le. The conical terminatiojj 

 of the spring shoot is now densely covered with the delicately fringed bracts inclosing the buds of 

 the foliage leaves, which impart to it the appearance of a silvery white tuft, by which this species 

 is recognized at first sight. 



Daring tlie following two years the growth proceeds but slowly, the length by the end of the 

 fourth year averaging not more than 5 inches with a thickness of three fourths to seven-eighths 

 of an inch. During the same time the taproot is found to gain constantly both in thickness and 

 length (see PI. VII, e). A few single branches now make their appearance on the main axis. 

 The increase of growth from one season to another up to the seventh or eighth year is difQcult to 

 follow, since the ditterence in the appearance of the spring and summer wood cells in the spongy 

 -wood of young trees is hardly perceptible, and the rings of annual growth, even as seen in cro'ss 

 sections prepared for micro <coi)ical examination, are mostly too indistinct to afiord a safe criterion 

 of their age. As far as could be observed the growth proceeds equally slowly during the fifth and 

 sixth years, the plant at the end of that period being from 5 to 7 or 7.i inches in length. 



Stage of rapid growth.— With its seventh year the tree may be said to enter on its most 

 vigorous growth. Henceforth the stem (primary axis) increases rapidly iu length, and the 

 development of branches (lateral axes) proceeds at an equal rate iu regular whorls, to which the 

 symmetry of the tree in that stage of its development is due. During the seventh year, generally, 

 the tree doubles its length, and during a number of successive years the rate of growth iii that 

 direction varies between 10 and 20 inches annually, as is clearly shown by the length of the 

 internodes separating tlie whorls. As the branches increase iu length they produce, in the same 

 order mostly, two opposite secondary branches. With the rapid exi)ausion of tlie leaf surface, 

 the formation of wood keeps pace. The rate of growth in diameter, as well as in height, during 

 this period, is of course variable according to differences in the physical condition "of the soil 

 as well as in the available amount of plant food and moisture it contains, and no less upon 

 dilierences in temperature and of exposure to light and air. These variations are clearly shown 



