538 THE MICROSCOPE. 



parts of the plant ; in the stem, bark, leaves, stipules, 

 petals, fruit, root, and even in the pollen, with some 

 exceptions. They are always situated in the interior 

 of cells, and not, as stated by Raspail and others, in the 



Fig. 183. 



1, A section from the outer layer of the bulb of an Onion, showing crystals of 

 carbonate of lime. 3, Cells of the Pear, showing Sclerogen, or gritty tissue. 

 4, Cells of garden Rhubarb, filled with raphides. 5, Cells from same, filled 

 with starch-grains. 



intercellular passages. 1 Some of the containing cells be- 

 come much elongated ; but still the cell- wall can be readily 

 traced. In some species of Aloe, as, for instance, Aloe 

 verrucosa, with the naked eye we are able to discern small 

 silky filaments: when magnified, they are found to be 

 bundles of the acicular form of raphides, which no doubt 

 act the part of a stay or prop to the internal soft pulp. 



In portions of the cuticle of the medicinal squill 

 Scilla maritima several large cells may be observed, full 

 of bundles of needle-shaped crystal. These cells, however, 

 do not lie in the same plane as the smaller ones belonging 

 to the cuticle. In the cuticle of an onion every cell is oc- 

 cupied either by an octahedral or a prismatic crystal of 

 oxalate of lime : in some specimens the octahedral form 

 predominates ; but in others from the same plant the 



(1) "As an exception, many years ago they were discovered in the interior of 

 the spiral vessels in the stem of the grape-vine ; but with some botanists this 

 <rould not he considered as an exceptional case, the vessels being regarded as 

 elongated cells." Quekett. 



