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Vicia faba— movements of radicle on beans—

(Shows how apex wd behave with respect to stones in soil)

Placed bean with hilum upside in wet sand & turned it about when radicle protruded so that I made the point of the arched radicle come down on upper flat surface of bean at right angle. It then glided over the flat surface but the extreme apex did not appear hardly at all flattened. I then coated the surface with a thin layer of paste, made with lamp-black & water, but this was not furrowed!

Therefore it seems that though geotropism keeps the apex down, yet the point it is pressed with extremely little force on any opposing opposing object. Soon the extreme apex of the radicle turns up parallel to flat surface & bean, & here we see use of lateral upward nutation.—

I then fastened with fine ent: pins 2 little bits of wood, less than 1/20' of inch high., in front of apex & the 2 bits formed an open angle in front of gliding radicle.

The extreme transparent point after it had become into contact with the wood wa became a little flattened. In the course of 2° 30' the apex was obliquely flattened; & after 3°

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additional had moved to one side, so as to be in the angles between 2 bits of wood, & now the apex was not flattened, but perhaps a little blunter than before. Next morning (after 9° 30' intervals) the extreme apex was as sharp as ever & it was travelling laterally along a nearly horizontal surface, the apex in apposition with the opposing wood.

It never showed slightest tendency to move over the bit of wood 1/20' of inch high. It continued to move to considerable distance laterally & here we see use of lateral nutation, for if there had been no circumnutation the apex of root would have become doubled up, beneath in this case (& when it first came into contact with upper face of bean. I have said it move laterally on horizontal surface, but I rather think that there was at first a very slight inclination to the side to which the radicle bent after first coming into contact with wood. I then sloped the bean considerably, but the apex went on travelling upwards in opposition to geotropism in contact with wood, & this probably was due to distal portion now having got a permanent bend. When the apex came to square end of bit of

(over)

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wood & this was a considerably distance, it turned abruptly round it, & followed steep slope to edge of bean & then went perpendicularly down into sand.

I forgot to say that shortly after apex came into contact with wood, terminal part became more bowed, owing to growth on convex surface & no possibility of penetrating bean or travelling onwards

It does not appear that the actual apex grows, judging from spot of vermilion put on. It must be understood that bits of wood were placed nearly at right angles to the travelling radicle.—

(I remember that when I allowed tips to grow into shallow holes they forced themselves out & this shows necessity of downward pressure.— N.B. my measurement of transverse strain of radicle applies to some height above apex, f for it could not have bn measured, as so difficult to keep in Holes.)