xxiii.] BOTANY. 93 



duration. Amongst instances of fugacious vitality are 

 acorns, which germinate at once, and maple-seeds. 

 As a proved instance of persistent vitality, the sacred 

 bean of India is the most authentic ; one such taken 

 from a herbarium upwards of one hundred years old, 

 having germinated. Wheat is said to keep for seven 

 years at the longest. The statements as to mummy 

 wheat are wholly devoid of authenticity ; as are those 

 of the raspberry seeds taken from a Roman tomb. 

 On the other hand, that seeds may remain buried 

 alive in the soil for many years is rendered most 

 probable by the fact of charlock and broom appearing 

 suddenly and in quantities in newly-turned-up soil 

 that had not been disturbed for long periods. It is, 

 however, difficult to believe that such a moist complex 

 substance as living protoplasm can resist chemical 

 change sufficiently long to favour the idea that seeds 

 have lain buried alive in the soil for many hundred 

 years. 



XXIII. SURFACE COVERINGS AND APPEN- 

 DAGES. 



138. These are either exudations from the cells 

 of the epidermis (Par. 6), or modifications of the 

 epidermal cells, or cellular growths from them. They 

 serve very various and totally distinct functions, all 

 necessary to the health, growth, or propagation of the 

 plant. The principal of them may be most instruc- 

 tively classed under their apparent uses : 



(a) Protective. The simplest of all is the bloom 

 of the grape, cabbage-leaf, pea-pod, &c. It consists 

 of a secretion of wax, which being insoluble in water is 



