424 Chronicles of Science. [July, 



growth of Lemna minor had hcen allowed to accumulate on the 

 surface, a sudden death of all the fish in the water occurred, and the 

 smell of sulphuretted hydrogen was remarkably strong. On making 

 examination of the water by careful chemical analysis, M. Dehe- 

 rain found that there was absolutely no dissolved oxygen present, 

 hence the death of the fish. The aquatic pknts had been killed by 

 the exclusion of light caused by the Lemna growth, and they had 

 absorbed what oxygen was available, M. Van Tieghem, a very 

 distinguished French botanist, relates some interesting experiments 

 on the action of hght in the respiration of aquatic plants. He 

 maintains that the chlorophyl is brought into a condition com- 

 parable to that of a ijlwsphor^scent body by the action of direct 

 sunlight. It is direct sunlight only which is competent to staii 

 the decomposition of carbonic acid by the chlorophyl — as numerous 

 experiments prove, — diffused (polarized) sunlight not having that 

 power: when withdrawn fi'om direct sunhght and kept in the 

 dark, Van Tieghem observed that the plant still continued to exert 

 chemical action for three hours, and for nine hours if kept in dif- 

 fused dayhght instead of darkness. From this he concludes that 

 the vibrations mduced by the chemical rays of sunlight are con- 

 tinued in the chlorophyl after removal from then- contact, which is 

 indicated by the continued chemical action, just as light is con- 

 tinued by the sulphides of barium, &c. ; and he supposes that 

 diffused daylight, though incompetent to start this action, can assist 

 in continuing it. 



The Action of the Cuticle in the Respiration of Plants. — 

 M. Barthelemy has applied the results of Graham's researches on 

 dialysis of gases through colloid membranes to the case of plant- 

 respiration. In plants there exists a cuticle which has a chemical 

 composition and a physical constitution like caoutchouc. It is 

 wanting at the "stomata " which occm- on the under-sm-face of leaves. 

 The experiments of many observei-s, notably Boussingault, have 

 shown that the exhalation of oxygen is greatest when sunlight falls 

 on the ui^i^er surface of leaves. M. Barthelemy explains this by 

 supposing the resphation to take place through the cuticle, tlio 

 etomata perhaps absorbing nitrogen. The relative penneabihty of 

 caoutchouc to various gases agrees well with the hypothesis— car- 

 bonic acid passing most freely, oxygen also freely, and nitrogen 

 with difficulty. This view is further sup^wrted by ingenious experi- 

 ments, in which leaves were substituted for caoutchouc in experiments 

 similar to Mr. Graham's, and veiy fairly concordant results were 

 attained. 



Cephcdodia of Lichens. — Dr. Nylander makes some important 

 observations on these organs, which were but little known before he 

 pouited out their importance as furnishing a primary auatomical 

 character in their gonimia. They occur only in tlialli which have 



