432 



AMERICAN HOMES AND GARDENS 



November, 1907 



often noticeable that the plumule is somewhat more ad- 

 vanced in growth than the radicle. This advance, however, 

 is deceptive; for when we come to examine the next important 

 stage in the birth of the wheat (Fig. 7) we invariably find 

 that whereas the young shoot has made little growth, the 

 young root has extended in a surprisingly rapid manner* 

 Moreover, we notice that the tips of two more roots have 

 made their appearance — the first pair of adventitious roots 

 they are called; and we begin to realize, perhaps for the first 

 time, that the birth of the wheat is a complex matter, and 

 that we have as yet by no means seen the end of it. 



For the moment, however, the reader will do well to pay 

 exclusive attention to the primary root which has become so 

 suddenly elongated. The very fact of its rapid growth seems 

 to indicate its im- 

 portance, Indeed, 

 upon it devolves the 

 duty of obtaining 

 the increasing sup- 

 ply of moisture de- 

 m a n d e ci by the 

 germinating em- 

 bryo. It must pro- 

 cure, moreover, cer- 

 tain chemicals in 

 solution which are 

 requisite for build- 

 ing up the living 

 cell tissue of the 

 plant which is to be. 



So the primary 

 root goes down- 

 ward into the soil; 

 and at a v e r y 

 early age it de- 

 velops root hairs — 

 delicate white fila- 

 ments which spread 

 out at right angles 

 to the root. They 

 assist it In its search 

 for moisture; also, 

 by the i r passage 

 among the minute 

 particles of soil, 

 they probably add 

 materially to the 

 holding power of 

 the root — an im- 

 portant function in 

 view of wind, or 

 heavy rain, which might at any moment strain the anchorage 

 of the germinating seed. 



The most interesting part of this tiny root, however, is 

 its tip, or growing point. This is semi-liquid and transpar- 

 ent; yet it exhibits an exquisite sensitiveness which enables it 

 to avoid destruction and threatened injury, and to feel its 

 way between the particles of soil. One is tempted to endow 

 It in imagination with a species of Intelligence. "A radicle," 

 wrote Darwin, "may be compared with a burrowing animal, 

 such as a mole, which wishes to penetrate perpendicularly 

 down into the ground. By continually moving its head from 

 side to side, or circumnutating, he will feel any stone or 

 other obstacle, as well as any difference in the hardness of 

 the soil, and he will turn from that side; if the earth is 

 damper on one than on the other side, he will turn thither- 

 ward as a better hunting ground. Nevertheless, after each 

 interruption, guided by the sense of gravity, he will be able 

 to recover his downward course, and to burrow to a greater 

 depth." 



iO 



10 — The Beginning of the First Leaf 



1 2 — The Expansion of the First Leaf and the 



Furthermore, the root tip appears to be gifted with a cer- 

 tain power of selection — some of the chemicals dissolved in 

 the fluid which surrounds it being absorbed, and others being 

 rejected. Thus, if we plant a pea and a grain of wheat in 

 the same soil, the root tip of the former will hunt about for 

 and take up whatever calcareous substances the water of the 

 soil contains. But the root tip of the wheat will reject these, 

 and obtain for itself all the silex, or flinty matter, afforded 

 by the soil; and it is the deposition of this silex in the stem 

 which gives to all grasses so much firmness, enabling them 

 to withstand wind pressure, and to raise their flowerheads to 

 the sunlight, high above the surrounding herbage. There 

 Is enough silex in a wheat straw to make a bead of glass, 

 when melted with potash with the aid of a blowpipe. The 



pea, on the other 

 hand, being one of 

 those plants which 

 clamber over and 

 support themselves 

 upon other vegeta- 

 tion, does not re- 

 quire silex for 

 strengthening i t s 

 stems. 



We may form a 

 mind picture, then, 

 of the primary root 

 tip of the baby 

 wheat plant work- 

 ing its way among 

 the particles of soil, 

 generally with a 

 d O' w n w a r d ten- 

 dency, but turning 

 aside from obstacles 

 In its path, and 

 moving hither and 

 thither in its search 

 for moisture and 

 such chemical sub- 

 stances as it ma y 

 need. Moreover, the 

 primary root tip is 

 not left long to 

 labor alone. We 

 have already seen 

 ( Fig. 7) the forma- 

 tion of two adven- 

 titious root sheaths; 

 and from these 

 shortly issue and 

 pass downward into the soil the first pair of adventitious 

 roots, which soon produce root hairs and exhibit all the char- 

 acteristics which we have observed in the case of the primary 

 root. The condition of the grain at this stage is shown at 



Fig. 8- . . . 



In examining this photograph the reader will observe that 

 the plumule has made comparatively little progress. But, as 

 the three roots continue to work their way into the soil, the 

 tiny plant begins to feel its power — if we may so express it — 

 and the pale yellow plumule grows more rapidly upward in 

 the direction of the free air and light. The plumule is not, in 

 itself, a leaf; it is a sheath which enfolds and protects the 

 delicate first green leaf of the wheat which we shall event- 

 ually see produced. Even now this leaf, complete in every 

 detail, lies packed within the plumule; but the status of the 

 plant is not yet sufficiently assured to warrant its produc- 

 tion. So the plumule moves upward, while the three roots 

 continue to burrow more deeply into the soil. 



And now we note the commencement of yet another 



12 



I I — The Growth of the First Leaf : no Expansion 

 Development of the Sixth Adventitious Root 



