INTRODUCTION. 



nothing will prevent a plant from shedding its leaves nearly at 

 its usual time ; and although by artificial heat, or by removal to 

 a warmer climate, a new crop can be brought out within a short 

 interval, this exhausts its powers, so that few kinds can survive 

 the change of circumstances for any long period. Moreover, the 

 period of inactivity cannot in these cases be prolonged beyond a 

 certain fixed time ; for a plant, whose growth in spring is checked 

 by the protracted influence of cold, loses its vitality altogether. 

 But there are some instances in which this condition may be 

 greatly prolonged. Bulbs, for example, of the onion, hyacinth, 

 tulip, &c. have been kept for many years in this dormant state, 

 capable of renewing the active processes of vegetation, of 

 shooting up leaves and flower-stems into the air, and of trans- 

 mitting their roots into the soil for many years; and there does 

 not seem any particular limit to this power. Instances have 

 been related of the growth of bulbs unrolled from among the 

 bandages of Egyptian mummies ; but there is reason to believe 

 that deception has been practised on this point upon the too- 

 ready credulity of travellers, still there is nothing impossible in 

 the asserted fact. Light, warmth, and moisture are the causes 

 of the growth of these curious structures ; and when removed 

 from the influence of these, there is no reason why a bulb should 

 not remain unchanged for 100 years, if it can for 10; and for 

 JOOO, if for 100. We shall hereafter see that the vitality 

 of seeds under similar circumstances appears quite unlimited. 

 (Chap, xii.) 



But there are some plants which, even whilst in a state of 

 active vegetation, are capable of being reduced to a similar torpid 

 condition, and of remaining in it for almost any length of time, 

 without injury to life. There is a kind of Club-Moss inhabiting 

 Peru, which is liable to be entirely dried up, when deprived of 

 water for some time. It then folds in its leaves and contracts 

 its roots, so as to form a ball, which, apparently quite devoid of 

 animation, is driven about hither and thither by the wind ; as 



