CELL-CONTENTS. 



421 



latter observer, the needle-shaped or acicular are composed of phos- 

 phate, and the stellate of oxalate of lime. There are others having 

 lime as a basis, combined with tartaric, malic, or citric acid. These 

 are easily destroyed by acetic vacid ; they are also very soluble in many 

 of the fluids employed in the conservation of objects ; some of them 

 are as large as the l-40th of an inch, others are as small as the 

 l-1000th. They occur in all parts of the plant; in the stem, bark, 

 leaves, stipules, sepals, petals, fruit, root, and even in the pollen, with 

 few exceptions. They are always situated in the interior of cells, and 

 not, as has been stated by Raspail and others, in the intercellular pas- 

 sages.* Some of the containing cells become much elongated j but still 

 the cell-wall can be readily traced. In some species of Aloe, as, for 

 instance, Aloe verrucosa, with the naked eye you will be able to discern 

 small silky filaments. When these are magnified, they are found to be 

 bundles of the acicular form of raphides. 



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 



fig. 202. 



1. A Transverse section of stem of Equisetum, showing the hexagonal shape of cells. 

 2. A vertical section, showing the elongated cell. 3. Cells of the Pear, showing 

 Sclerogen, or gritty tissue. 4. Cells of garden Khubarb, filled with raphides. 5. 

 Cells from same, filled with starch-grains. 



cell is occupied either by an octahedral or a prismatic crystal of oxalate 

 of lime : in some specimens the octahedral form predominates ; but in 



* 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 would not be 

 considered as an exceptional case, the vessels being regarded as elongated cells. 



