Little squares of the card-like paper were next affixed to radicles of the pea at 4 mm. above the apex, in the same manner as with the bean.  Twenty-eight radicles suspended vertically over water were thus treated on different occasions, and 13 of them became curved towards the cards.  The greatest degree of curvature amounted to 62o from the perpendicular; but so large an angle was only once formed.  On one occasion a slight curvature was perceptible after 5 h. 45 m., and it was generally well-marked after 14 h.  There can therefore be no doubt that with the pea, irritation from a bit of card attached to one side of the radicle above the apex suffices to induce curvature.

Squares of card were attached to one side of the tips of 11 radicles within the same jars in which the above trials were made, and five of them became plainly, and one slightly, curved away from this side.  Other [page 158] analogous cases will be immediately described.  The fact is here mentioned because it was a striking spectacle, showing the difference in the sensitiveness of the radicle in different parts, to behold in the same jar one set of radicles curved away from the squares on their tips, and another set curved towards the squares attached a little higher up.  Moreover, the kind of curvature in the two cases is different.  The squares attached above the apex cause the radicle to bend abruptly, the part above and beneath remaining nearly straight; so that here there is little or no transmitted effect.  On the other hand, the squares attached to the apex affect the radicle for a length of from about 4 to even 8 mm., inducing in most cases a symmetrical curvature; so that here some influence is transmitted from the apex for this distance along the radicle.

Pisum sativum (var.  Yorkshire Hero):  Sensitiveness of the apex of the Radicle.—­Little squares of the same card-like paper were affixed (April 24th) with shellac to one side of the apex of 10 vertically suspended radicles:  the temperature of the water in the bottom of the jars was 60o — 61o F. Most of these radicles were acted on in 8 h. 30 m.; and eight of them became in the course of 24 h. conspicuously, and the remaining two slightly, deflected from the perpendicular and from the side bearing the attached squares.  Thus all were acted on; but it will suffice to describe two conspicuous cases.  In one the terminal portion of the radicle was bent at right angles (A, Fig. 66) after 24h.; and in the other (B) it had by this time become hooked, with the apex pointing to the zenith.  The two bits of card here used were .07 inch in length and .04 inch in breadth.  Two other radicles, which after 8 h. 30 m. were moderately deflected, became straight again after 24h.  Another [page 159] trial was made in the same manner with 15 radicles; but from circumstances, not worth explaining, they were only once and briefly examined after the short

Fig. 66.  Pisum sativum:  deflection produced within 24 hours in the growth of vertically dependent radicles, by little squares of card affixed with shellac to one side of apex:  A, bent at right angles; B, hooked.