THE NATURAL CONDITIONS OF PLANTS. 87 
a seedling fern and a grass made their appearance 
on the surface of the mould. 
I could not hut he struck with the circum- 
stance of one of that very trihe of plants which I 
had for years fruitlessly attempted to cultivate, 
coming up sponte sud in such a situation, and 
asked myself seriously what were the conditions 
necessary for its well-being ? To this the reply 
was — a moist atmosphere free from soot or other 
extraneous f articles ; light ; heat; moisture; periods 
of rest ; and change of air. All these my plant 
had ; the circulation of air being obtained by the 
diffusion law already described. 
Thus, then, all the conditions requisite for the 
growth of my fern were apparently fulfilled, and 
it remained only to test the fact by experiment. 
I placed the bottle outside the window of my 
study, a room with a northern aspect, and to my 
great delight the plants continued to thrive. They 
turned out to be L. Filix mas and the Poa annua. 
They required no attention of any kind, and 
there they remained for nearly four years, the 
grass once flowering, and the fern producing 
three or four fronds annually. At the end of 
this time they accidentally perished, during my 
absence from home, in consequence of the rusting 
of the lid, and the consequent too free admission 
of rain water. Long before this occurred, how- 
