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Sept 2d. 1878 Cassia— sea-side sp (Relative Darkness)

S. Tosa.

Seedlings with cots placed in S.W window bright, but cloudy day with short gleams of sun, for 32' & then placed on study table & cots rose so much as almost to deserve to be called asleep; afterwards awake on study table. — Another pot put behind study screen & left there for 32', when cots much closed; put on study table & 10' more were still more closed— so that one pair had the 2 Cots forming angle together of 19°. — Whether the cotyledons which had been behind screen or those exposed to bright sun wake first on my study table I did not accurately ascertain, but I believe those behind screen.

[1v]

[calculations not transcribed]

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Sept. 3' 1878. Cassia (sea-side sp) C. Tosa

Two pots in my study with horizontal cots—

(1) Pot placed in dull sunshine under Bell-glass from 7° 38' a.m to 9° 36' i.e. for 2 Hours.— & then put on my middle Study Table. At 10° 30 26' (ie after 1°— 50' on on my table, the 2 Cots of (1) seedling instead of forming together an angle of 180°, formed an angle of only 43°, so that each cot. had risen 68 1/2° owing to the change from dullish sunshine to the light in middle of N.E not dark room.

A second seedling treated in all respects the same each cot rose or close 66 1/2°. After 30' additional time the cots of both seedlings began to open again

The second pot of seedlings with Cots. horizontal in Hothouse my study was put at same time & for same time behind screen of books in my study & therefore were very feebly illuminated. After 2°, the Cots. of (1) seedling instead of forming angle of 180°, had closed or risen so that they formed together angle of 63°. Therefore each cot. had risen in the feeble light 58 1/2°

When placed on study Table (close to previous pot, which had been in sun)

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Under the exactly same degree of light some seedlings were lowering & other raising their cotyledons.

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Cassia

in the course of 1° 50' the cots. opened & formed together an angle of 114°; so that each cot had opened or fallen 25 1/2°.

A second seedlings treated in exactly same manner its cots rose, so that each rose 63 1/4° & after 1° 50' on study Table opened or fell 32 3/4°.

There was a conspicuous difference at 10° 30' between all the seedlings in the 2 pots.— As few some few seedlings of other plants raise sink their cots in dark the result cannot here be any direct action of light— or rather darkness & we learn certainly that it is relative degree of darkness, & not any absolute intensity want of light which causes movement.—

Seeing how wonderfully sensitive the Cots are to light, it is remarkable that the Hypocoty of this Cassia is very little sensitive & bends far less to light than most plants.—

[3v]

On the action of relative Light in affecting Periodical movements & on inheritance of Sleep-movements

Introduce either in chapter on sleep of Cotyledons or on Sleep of Leaves