FORM AND ARRANGEMENT OF CELLS. 5 



(fig. 20 a a). When porous cells are united end to end, so as to 

 form tubes, they have been denominated articulated Bothrenchyma 

 (/3o0go;-, a pit), on account of the pits or depressions in their thickened 

 walls (fig. 22). 



11. Fibrous OP Spiral cells are those in which there is a spiral 

 elastic fibre coiled up in the inside of the membrane (fig. 23). When 

 united, they form fibro-cellular tissue, or Inenchyma (his, fibres). These 



cells generally consist of membrane and fibre combined, but the 

 former appears to be sometimes absorbed wholly or partially during 

 the progress of growth. The membrane, in some instances, is easily dis- 

 solved by water, and then the elastic close convolutions of the fibre spring 

 out with considerable force, as in the outer covering of the seeds of 

 Collomia and Salvia. Spiral cells abound in many of the Orchidaceous 

 plants, 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 seed of Acanthodium spicatum. The 

 spiral filaments sometimes exhibit peculiar movements when placed 

 in water. The fibre varies from about 55 ^o to 10,000 f an mcn m 

 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), scalariform and dotted cells (fig. 26), which 

 constitute the spurious or imperfect Inenchyma of authors. 



12. In certain parts of plants cells are placed closely together, and 

 compressed so as to touch each other by flat surfaces, filling up space 

 completely, and leaving no intervals; they then form the perfect Paren- 

 chyma 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 imperfect 

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

 ate size and continuous, are called intercellular passages or canals; when 

 large, irregular, and circumscribed, intercellular spaces, or Lacunae (fig. 

 16 1 1). 



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



Figs. 23, 24, 25. Spiral, annular, and reticulated cells, from Misletoe (] 7 iscitm album). 

 F'g. Id.' Scalarifbrm and dotted cells, from Elder (Sanibucus niyra). 



