54 THIRD REPORT — '1833. 



The same principle of growth appears to obtain in Confervas, 

 and probably is found in other vegetables of the lowest grade. 



This is analogous to what takes place in the formation of the 

 embryo of Vasciilares. In the opinion of Dr. Brown and of 

 Mirbel, the first rudiment of a plant far more comphcated than 

 Marchaniia, consists also of a vesicle, but suspended by a 

 thread to the summit of the cavity of the ovulum ; and the dif- 

 ference between the one case and the other is, that while in the 

 Marchaniia the original vesicle, " as soon as it is formed, pos- 

 sesses all the conditions requisite for developing a complete 

 plant on the surface of the soil ; on the other hand, that of 

 flowering plants must, on pain of death, commence its deve- 

 lopment in the interior of the ovulum, and cannot continue it 

 further until it has produced the rudiments of root, stem, and 

 cotyledons*. 



Beyond this I do not think that any attempt has been made 

 to elucidate the question. 



Irritability. — I3r. Dutrochet has published f the result of 

 some experiments v,ith the air-pump upon the pneumatic system 

 of plants. Independently of confirming the fact, already gene^ 

 rally known, of plants having the means of containing a large 

 quantity of air, he arrived at the unexpected result, that the 

 sleep of plants and their irritability are certainly dependent upon 

 the presence of air within them. A sensitive plant, left in the 

 vacuum of an air-pump for eighteen hours, indicated no sign 

 whatever of the accustomed collapse of its leaflets on the ap- 

 proach of night, nor when it was restored to the air could it be 

 stimulated by the smartest shocks ; but in time it recovered its 

 irritabihty. When flowers that usually close at night were 

 placed in a vacuum while expanded, they would not close ; and 

 when flowers already closed were placed in the same situation, 

 they would not unfold at the return of morning ; whence Dr. 

 Dutrochet infers that the internal air of plants is indispensably 

 necessary to the exercise of their alternate motions of sleeping 

 and waking, and in general to the existence of the faculty they 

 possess of indicating by their movements the influence of ex- 

 ternal exciting causes. 



Action of Coloured Light. — Professor Morren, of Ghent, lias 

 mentioned j the result of some experiments upon the action of 

 the coloured rays upon germination ; and he has fovmd that 

 while those rays in which the illuminating power is the most 

 feeble were, as might have been expected, the most favourable 

 to germination, their power of decomposing carbonic acid, and 



* Archives de Botanique, vol. i. t ■•'innalcs des Sciences, vol.xxv. p. 243. 

 J Annates des Sciences, vol. xxvii, p. 201, 



