FORM AND ARRANGEMENT OF CELLS. 7 



abound in many of the Orchidaceous plants, as Oncidium and 

 Pleurothallis ruscifolia, also in the garden Balsam, in the leaf of the 

 moss called Sphagnum, and in the Cactus tribe. They are also found in 

 the inner covering of anthers, in the spore-cases of many of the lower 

 tribes of plants, and in the coats of the seeds of Acanthodium spica- 

 tum, Sphenogyne speoiosa, Calempelis scaber, and Oobsea. The spiral 

 filaments sometimes exhibit peculiar movements when placed in water. 

 The fibre in these cells varies from about twu-u to -mhr^ of an inch 

 in diameter ; it is solid, and presents either a circular, an elliptic; or 

 a quadrangular section. The coils of the fibre sometimes separate 

 from each other, and become broken up and united in various ways, 

 so as to appear in the form of rings, bars, or dots, thus giving rise to 

 annular (fig. 24), reticulated (fig. 25), sealariform and dotted cells 

 (fig. 26), which constitute the spurious or imperfect Inenchyma of 

 authors. Annular cells are met with hi Opuntia, and in the endothe- 

 cium of Cardamine pratensis ; reticulated cells, caused by fibres forming 

 a sort of mesh or network, are seen in the wing of the seed of Swietenia, 

 the pericarp of Picridium tingitanum, the leaf of Sanseviera guineensis, 

 and the pith of Eubus odoratus and Erythrina Corallodendron, as well 

 as in the endothecium of the sea-pink and the butterwort. 



In certaia parts of plants cells are placed closely together, and 

 touch each other by flat surfaces, filling up space completely, and 

 leaving no intervals ; they then form the .perfect Parenchyma of 

 Schleiden (figs. 8, 27). In lax tissues, however, the cells retain a 

 rounded shape, and then touch each other at certain points only, 

 leaving intervals of various sizes and shapes, and forming the imper- 

 fect Parenchyma of Schleiden (figs. 7, 28). These intervals, when of 

 moderate size and continuous, are called intercellular passages or canals ; 

 when large, irregular, and circumscribed, intercellular spaces, or Lacunm 



(fig. 16,Z0- 



Fig. 2T. Kg. 28. 



A difference of opinion prevails as to the mode in which cells 

 are united together. Some maintain that the cell-walls in the young 



Fig. 27. CelluJar tissue, from pith of Elder. Fig. 28. Porous merenciyma, from 

 Houseleelc ifim^ermAywm, tectonm). a, Intercellular canal. 



