40 



ON THE PLANT-CELL. 



History and Criticism. It is usual to distinguish a number of ele- 

 mentary organs in plants, and, although mostly regarded as forms of the 

 cell, yet Link and Treviranus adhere to three, the cell, the vessel, and 

 the fibre. It is, to say the least of it, unphilosophical to assume that 

 plants have three elements, and then to prove that all three are one and 

 the same. The pretended difference of function which confirms this 

 division is of no importance, as there is not so much difference of function 

 between vessels and cells as there is between two cells, the one of which 

 secretes a volatile oil and the other granules of starch. 



The milk-vessels (laticiferous tissue) which are covered with a proper 

 membrane have not, with certainty, been made out to originate in cells. 

 Their origin is obscure, and in their perfect state they resemble elon- 

 gated branched cells, and agree with these in the transition forms which 

 they exhibit in the progress of development. 



16. Up to a certain time the cell- wall grows in its entire 

 extent, through intus-susception, but not often uniformly. Indi- 

 vidual spots are more freely nourished, and form warty projections 

 upon the external or internal surface of the cell. 



It appears to me that the attention which this point deserves has not 

 been given to it. It has been long known that certain hairs possess 

 warts, which are clearly arranged in spiral lines. In most cases these 

 warts are small and uniform in size, as on the hairs of the families 

 Boraginece, UrticecB, Malvaceae^ &c. Sometimes, however, longer striped 

 elevations of the external surface are seen, as in the anther-hairs of Lobelia 

 cardinalis, the two-armed hairs upon the young branches of Cornus 

 mascula, &c. But the most striking thing about these warts is, that 

 they display one or two cavities in their interior, and are separated by a 

 definite line from the surface of the hair, as though they were adherent 

 cells. They are seen in the hairs of the throat of the species of Anchusa 

 (fig. 15.) and other plants. These warty excrescences are not confined 

 15 16 



to the external surface of hairs, but often form projections in the interior 

 of hairs, as, for instance, in the so-called root-hairs of Marchantiacece, in 

 the fibrous cells of Peltigera canina, in the spindle-shaped cells in the 

 style of Cereus phyllanthoides (fig. 16.), in the medullary rays of Pinus 

 sylvestris, in the hairs of Malpighiacece, where they form small peduncu- 



15 a, A hair from the nectary of Anchusa itaJica, covered with warts, b, c, d, Longi- 

 tudinal section of warts (e), as seen from above. 



16 Hair, with warts upon it, from Cereus phyllanthoides. The cell-walls are irregularly 

 thickened. 



