ON CLOSELY GLAZED CASKS, 215 



to grow ferns on rockwork in the yard at the back of his house, 

 and he could not but be struck with one coming up and growing so 

 well in a bottle. He asked himself seriously what were the conditions 

 necessary for its growth. " To this the answer was, lstly, an atmo 

 sphere free from soot (this I well knew from previous experience) ; 

 2ndly, light ; 3rdly, heat ; 4thly, moisture ; and lastly, change of air. 

 It was quite evident that the plants could obtain light and heat as 

 well in the bottle as out of it ; and that the lid which retained the 

 moisture likewise excluded the soot. The only remaining condition 

 to be fulfilled was the change of air ; and how was this to be effected ?" 

 The answer is, by the law of the diffusion of gaseous bodies, alluded 

 to in the preceding paragraph ; the crevices in the glass case admit- 

 ting of the exit and entrance of air, but not of the entrance of fuligi- 

 nous matter. This is the whole secret of the growth of plants in 

 glass cases. 



Mr. Ward observes, " The simple yet comprehensive principle on 

 which plants are grown in closed cases does not appear to be clearly 

 understood, and the object of the treatise is to remove erroneous notions 

 respecting it. This self-imposed task is most beautifully and philo- 

 sophically executed under the following heads : — I. On the Natural 

 Conditions of Plants. II. On the Causes which interfere with the 

 Natural Conditions of Plants in large Towns, &c. III. On the Imi- 

 tation of the Natural Conditions of Plants in closelv glazed Cases. 

 IV. On the Conveyance of Plants and Seeds on Ship-board. V. On 

 the Application of the closed Plan in improving the Condition of the 

 Poor. VI. On the probable future Application of the preceding 

 Facts. 



On Natural Conditions of Plants. — Plants are influenced by the 

 atmosphere, heat, light, moisture, varieties of soil, and periods of rest. 

 The effect of an impure, as compared with a pure atmosphere, is 

 exemplified in the plants which grow in large towns, or within the 

 reach of manufactures evolving noxious gases, as compared with those 

 which grow in the open country. Plants grow in different degrees of 

 heat, from 32° to 110° or ISO , in which last temperature certain 

 Cacti alone are found to live. The intensity of light to which plants 

 arc subjected varies from almost total darkness to a light double that 

 of our brightest summer's day. The state of atmospheric moisture 

 varies as much as those of atmospheric heat and light. All plants 



