Primula Sinensis (Primulaceae).—­A seedling was placed with the two cotyledons parallel to a north-east window on a day when the light was nearly uniform, and a filament was affixed to one of them.  From observations subsequently made on another seedling with the stem secured to a stick, the greater part of the movement shown in the annexed figure (Fig. 33), must have been that of the hypocotyl, though the cotyledons certainly move up and down to a certain extent both during the day and night.  The movements of the same seedling were traced [page 46] on the following day with nearly the same result; and there can be no doubt about the circumnutation of the hypocotyl.

Fig. 33.  Primula Sinensis:  conjoint circumnutation of hypocotyl and cotyledon, traced on vertical glass, from 8.40 A.M. to 10.45 P.M.  Movements of bead magnified about 26 times.

Cyclamen Persicum (Primulaceae).—­This plant is generally supposed to produce only a single cotyledon, but Dr. H. Gressner* has shown that a second one is developed after a long interval of time.  The hypocotyl is converted into a globular corm, even before the first cotyledon has broken through the ground with its blade closely enfolded and with its petiole in the form of an arch, like the arched hypocotyl or epicotyl of any ordinary dicotyledonous plant.  A glass filament was affixed to a cotyledon, .55 of an inch in height, the petiole of which had straightened itself and stood nearly vertical, but with the blade not as yet fully expanded.  Its movements were traced during 24 ½ h. on a horizontal glass, magnified 50 times; and in this interval it described two irregular small circles; it therefore circumnutates, though on an extremely small scale.

Fig. 34.  Stapelia sarpedon:  circumnutation of hypocotyl, illuminated from above, traced on horizontal glass, from 6.45 A.M.  June 26th to 8.45 A.M. 28th.  Temp. 23-24o C. Movement of bead magnified 21 times.

Stapelia sarpedon (Asclepiadeae).—­This plant, when mature, resembles a cactus.  The flattened hypocotyl is fleshy, enlarged in the upper part, and bears two rudimentary cotyledons.  It breaks through the ground in an arched form, with the rudimentary cotyledons closed or in contact.  A filament was affixed almost

* ‘Bot.  Zeitung,’ 1874, p. 837. [page 47]

vertically to the hypocotyl of a seedling half an inch high; and its movements were traced during 50 h. on a horizontal glass (Fig. 34).  From some unknown cause it bowed itself to one side, and as this was effected by a zigzag course, it probably circumnutated; but with hardly any other seedling observed by us was this movement so obscurely shown.