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PHYTOGENESIS. 245 Spiral faserzellen, &e., pp. 7, 8) is based upon inaccurate observation.

These cells are at first generally filled with starch; rarely with mucus or gum. The starch always passes into the latter substance in the progress of development; and this is converted into jelly, the change, as it would seem, taking place from without inwards. This jelly finally is converted at its outer surface into vegetable fibre, following the direction of a spiral line, the coils of which are sometimes narrower, sometimes wider. When these forms are observed in their different stages of development and in their various conditions, the idea involuntarily forces itself upon the mind that the spiral formation is the result of a spiral movement of a fluid on the walls of cells between them and the central jelly. Horkel once actually observed the motion of small globules between the coils of the fibre in progress of formation in Hydrocharis.

The great variety in the appearance of the fibres seems to depend upon the period of their origin, and on modification in the chemical changes of the formative material. It probably depends solely upon the former circumstance whether the spiral fibre lies free in the cell, when it is formed very late, or whether it is blended with the membrane of the cell, if its development commence at a period when the cell-membrane –itself is yet very soft and gelatinous, and may consequently become agglutinated to the fibre, which is likewise still in a gelatinous state. This is the case in Casuarina, Cassytha, Hydrocharis, Trichocline, Orchis, &c.; in most cases, however, the cell-wall is too far developed to unite with the fibre, and the latter then lies loose in the interior of the cell. In rarer instances the material is almost entirely applied to the formation of the fibre (always indeed when the fibre coalesces with the wall), for example, in Salvia Spielmanni, Momordica elaterium. I have reason to suppose that this complete consumption almost always takes place in spiral vessels, and is the cause of their subsequently conveying only air. More frequently, however, one or more fibres are formed; but then a great portion of the jelly has still remained uncon-