66 



THE TISSUES OF PLANTS 



Museum of the College of Surgeons, London, all the prin- 

 cipal varieties of the deposit of sclerogen are classified and 

 described under the name of hard tissues, and contrasted 

 with bone and teeth which form the hard tissues of 

 animals."* 



Earthy deposits sometimes occur in the cells of plants 

 in the form of crystals or raphides. These consist of inor- 

 ganic matter, generally of some acid and its 'base, which 



Fig. 16. 



A portion of the outer layer of the bulb of SciUa maritima, having acicular 

 .raphides in some of its cells. 



has united and crystallized in the cells. There is nothing 

 surprising in the existence of these crystals. "We know 

 that acids are formed in the vegetable organs, and these 

 unite with the earths or bases taken up by the roots from 

 the soil, whilst they are suspended in the cell-sap. These 



* " Lectures on Histology, deliyered at the Royal College of Sur- 

 geons of England, in tlie session 1850-51, by John Quekett. 1852." 



