62 EFFECTS OP LIGHT. 



cially those occupied by invalids : for how can a physician, careful of 

 the health of his patient, permit the presence of objects which are thus 

 incessantly contaminating the air ? It may be true that plants destroy 

 oxygen gas and form carbonic acid ; but if everything that produces 

 that effect was also to be expelled, the patient herself must be 

 separated from herself, for a human being consumes more oxygen, and 

 gives off more carbonic acid, in five minutes, than aU the plants in. a 

 sitting-room in twenty-four hours. It is wonderful that this notorious 

 fact should not have removed the prejudice about plants deteriorating 

 the air of sitting-rooms. It is still more surprising that the idea 

 should be retained at the present day, at least when it is also well 

 known that plants, in fact, purify instead of vitiating the atmosphere. 

 If it is true that they do a minute amount of harm, by destroying some 

 vital air, and producing some fixed air, it is equally true that they do 

 a great amount of good by producing a large quantity of vital air, and 

 destroying a large quantity of fixed air. It is one of the most beautiful 

 provisions we know of in nature, that the deleterious air breathed forth 

 by animals is purified and rendered salubrious by plants ; if it were 

 otherwise, the globe would become uninhabitable. But every leaf, 

 every blade of grass — ^nay, the finest of the green silken threads that 

 float about in pools of water, is incessanliy occupied, during daylight, 

 in effecting this most important change of pestilent air into an atmo- 

 sphere of life. One thing, however, is to be observed regarding plants. 

 Although it is false that they contaminate the air of a sitting-room, in 

 the way that is supposed, or in any other way, in the majority of cases, 

 yet it is certain that unpleasant effects are occasionally produced upon 

 peculiar constitutions by their odour. The flowers of the glaucous 

 Magnolia are said, to bring on sickness and headache ; the Jonquil, the 

 Tuberose, and the Lilac, are apt to cause faintness — an effect, indeed, 

 which we have seen produced by a few Violets, even in the open air ; 

 and Linnseus mentions a case of death, said to have been occasioned by 

 sleeping in a room where the Oleander was in flower. But this class of 

 effects does not in any way justify the exclusion of all plants from 

 sitting-rooms ; it only shows the necessity of avoiding the presence of 

 such as have powerful and oppressive odours. 



But, while this is true as a general axiom, it is necessary 

 to observe that some plants are naturally inhabitants of shady 

 situations, and are so organised as to be fit for such places and 

 for no others : plants of this description will not endure full 

 exposure to the sun ; not because an abundant decomposition 

 of carbonic acid is otherwise than favourable to them but 

 because their epidermis allows the escape of water too freely by 

 insensible perspiration, under the solar stimulus. 



