CUTICLE OF HYACINTH. 21 



way in which it has been naturalised and made most useful 

 in 'Sicily is remarkable. As soon as a little fissure is per- 

 ceived in the lava, a small branch or joint of Opuntia is 

 stuck in ; the latter pushes out roots, which are nourished 

 by the rain which collects round them, or by whatever 

 dust or remains of organic matter may have made a little 

 soil. These roots spread out and ramify into the most 

 minute crevices, breaking up the lava into small fragments, 

 and finally rendering it fit for culture. 



LITHOSPERMUM. 



From litlios a stone, sperma a seed. 



The hard stony seeds have given it this name, as well 

 as the old English appellative Gromwell, from the Celtic 

 yrom, a seed, and mil, a stone. 



The leaf of this common plant is extremely beautiful ; 

 the hairs are not only bulbous as in borage, but cells are 

 grouped around the base of each like a circlet of crystals. 

 There are three species worth seeking : 



The common white L. arvense, iri cornfields. 



L. officinalis, pale yellow. 



L. purpurea, large blue flowers in chalky soil. 



RAPHIDES. 



These are crystals found in the cells of various plants. 

 No better example can we have than the 



CUTICLE OF HYACINTH, 



in every cell of which we see a cylindrical crystal. Exa- 

 mined with polarized light they are most distinctly seen, 

 and enable us to understand the position of raphides in 

 other plants. The Cactus, the common Dock, and various 

 other vegetables, have bundles of needle-shaped crystals 

 in their cells. Turkey Rhubarb and the garden Rhubarb 

 have rectangular prisms of carbonate of lime grouped in a 

 stellate form. See the slide of 



