44 



ON THE PLANT-CELL. 



b. When simple or compound spirals do not grow together and form 

 rino-s, but the cell continues to grow, the spirals are then found in the 

 cell more or less free (Cellulce spiriferce) (fig. 19.). 



c. When many fibres grow together longitudinally, or the individual 

 turns unite at different points, and the cell grows rapidly, the free parts 



19 



of the fibres are drawn away from each other. The more numerous the 

 points of adhesion, the less the cell extends itself, the firmer grow the 

 fibres to the cell- wall * (Cellulce retiferce) (fig. 2023.). 



20 



22 



B. When the cells, from the first moment at which the spiral fibres 

 are produced, cease to extend, the turns of the spire grow firmly together 

 to the original walls of the cell. In this case the fibres touch each other 

 at countless points, and grow together. It is seldom that the spires 

 unite throughout their whole length to form a homogeneous layer ; yet 

 this occurs sometimes, as seen in the cells of the liber of the Flax and the 

 Lime ( Tilia europed]. This sometimes takes place on one side of a cell, 

 whilst the other exhibits a formation of pores, as in the rows of great 

 porous cells in the vascular bundles of Monocotyledons. In most cases, 

 however, the spires grow together at particular points, leaving between 

 them smaller or larger openings in the disunited spaces (fig. 23.). Fre- 

 quently the corners of these openings become rounded by the deposition 

 of fresh matter, and the original chink appears as a little pit in the deposit- 

 layer (fig. 24.). In tolerably thick deposit-layers this pit, by a transverse 

 section, may be observed as a narrower or wider canal (fig. 24.), which 

 sometimes gradually or suddenly opens at the outside of the wall of the 



* To this form belongs the branched spiral of authors. 



19 A fibrous cell, with 1 3 pure spiral bands ; a seen from the side, b and c from 

 above. These cells are found under the epidermis of the leaves of Pleurothallis rusci- 

 folia. 



20 Fibrous cells, with netted fibres, formed from a spiral, as seen in the veins of the 

 leaves of Gesneria latifolia. 



21 Netted fibrous cells, from the back of the root of Maxillaria atropiirpurea. 

 88 The same from the root of Acropera Loddigesii. 



