=248. Roots of the pumpkin.=—The seeds, a handful or so, are soaked in water for about 12 hours, and then placed between layers of paper or between the folds of cloth, which must be kept quite moist but not very wet, and should be kept in a warm place. A shallow crockery plate, with the seeds lying on wet filter paper, and covered with additional filter paper, or with a bell jar, answers the purpose well.
The primary or first root (radicle) of the embryo pushes its way out between the seed coats at the small end. When the seeds are well germinated, select several which have the root 4-5 _cm_ long. With a crow-quill pen we may now mark the terminal portion of the root off into very short sections as in fig. 110. The first mark should be not more than 1 _mm_ from the tip, and the others not more than 1mm apart. Now place the seedlings down on damp filter paper, and cover with a bell jar so that they will remain moist, and if the season is cold place them in a warm room. At intervals of 8 or 10 hours, if convenient, observe them and note the farther growth of the root.
[Illustration: Fig. 110. Root of germinating pumpkin, showing region of elongation just back of the tip.]
=249. The region of elongation.=—While the root has elongated, the region of elongation _is not at the tip of the root. It lies a little distance back from the tip_, beginning at about 2mm from the tip and extending over an area represented by from 4-5 of the millimeter marks. The root shown in fig. 110 was marked at 10 A.M. on July 5. At 6 P.M. of the same day, 8 hours later, growth had taken place as shown in the middle figure. At 9 A.M. on the following day, 15 hours later, the growth is represented in the lower one. Similar experiments upon a number of seedlings give the same result: the region of elongation in the growth of the root is situated a little distance back from the tip. Farther back very little or no elongation takes place, but growth in diameter continues for some time, as we should discover if we examined the roots of growing pumpkins, or other plants, at different periods.
=250. Movement of region of greatest elongation.=—In the region of elongation the areas marked off do not all elongate equally at the same time. The middle spaces elongate most rapidly and the spaces marked off by the 6, 7, and 8 _mm_ marks elongate slowly, those farthest from the tip more slowly than the others, since elongation has nearly ceased here. The spaces marked off between the 2-4 _mm_ marks also elongate slowly, but soon begin to elongate more rapidly, since that region is becoming the region of greatest elongation. Thus the region of greatest elongation moves forward as the root grows, and remains approximately at the same distance behind the tip.