214 Gruithuisen's City in the Moon. 



appear to oppose some resistance to their transit, and may be 

 stretched in consequence. The utricles, floating freely in the 

 water, become the seat of endosmotic and chemical actions, 

 especially when the surrounding water has a temperature of 

 from 16° to 15° (0). The utricles enclose at the beginning a 

 mucilaginous liquid, in which a gas-bubble soon appears, and 

 increases in size : this is the oxygen evolved under the influence 

 of light and heat. The plant disengages itself from the soil, 

 and mounts towards the surface ; the secretion of gas becomes 

 more abundant, and the flower-stems are raised above the 

 water. The oxygen secreted in the air-vesicles seems to 

 exercise a chemical influence in changing the colour of the 

 cell-walls, which become rose, lilac, and blue. The colouration 

 of the envelope affects the internal processes of the cell. We 

 know that in organs not coloured green, like the petals of a 

 flower, there is no evolution of oxygen, but an absorption of 

 oxygen and an evolution of carbonic acid. This gas does not 

 leave. the utricle, but is probably assimilated there; the utricle 

 becomes again filled with mucilage, and water which it absorbs 

 augments in weight and causes it to descend. Thus the 

 utricles have a respiratory as well as a hydrostatic function. 



GBUITHUISEN'S CITY IN THE MOON.— JUPITER'S 

 SATELLITES.— OCCULTATIONS. 



BY THE EEV. T. W. WEBB, A.M., E.K.A.S. 



We will now, in continuation of our subject, direct our 

 attention to the region lying S. and S.W. of the great clefts 

 recently described. — Dionysiiis (25), a small crater (14 miles 

 across, Lohrm.), lying on the shore of the M. Tranquillitatis, 

 and having perhaps 3800 f. of depth, or more than enough to 

 hide the peak of Snowdon, is chiefly remarkable on account of 

 its brilliancy, amounting to 7° for its interior, and 9° for its 

 wall. Yet it is not to be seen in the earth-shine, probably, 

 B. and M. remark, on account of its small dimensions. It 

 would be an interesting and not unpromising investigation, to 

 ascertain whether this is the true cause, and attended with no 

 great trouble, as it would not be difficult to select other small 

 crater3 which are perceptible on the dark Bide, and whose 

 magnitude would be comparable with that of Dionysius. I 

 have never made the attempt, but trust some of my readers 

 may have at once sufficient instrumental power and leisure to 

 take it in hand. We hav i that changes of colour, of 



