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PHYTOGENENSIS. 247 given rise to the conflicting views of authors. But the same also occurs in all cells under certain circumstances, and the influence of the spiral fibre remains meanwhile altogether obscure and unexplained. Perhaps the foregoing may render it probable that the spiral is everywhere only a secondary variation of form in the product of the vital power (the fibrin) produced by a different tendency of the vital activity of the cell, so soon as this is compelled, as a certain stage of its development, to give up its independent individuality, and enter as an integral portion into the complex of the entire plant.

I also think that we may venture, in conclusion, to deduce from the data above enumerated, that this indication of a spiral formation is the surest sign that we have no longer anything to do with the simple cell-membrane.

I now return, after this somewhat lengthy digression, to my subject. The process of cell-formation, which I have just endeavoured to describe in detail, is that which I have observed in most of the plants which I have investigated. There are, however, some modifications of this process which make the observation of many parts very difficult, and sometimes indeed render it impossible, although, notwithstanding this, the law remains undisturbed and universally valid, because analogy requires it, and we can fully explain the causes of the impossibility of direct observation.

The difficulties which I now notice depend especially upon the physical and chemical properties of the substance which precedes the formation of cells. The materials enumerated above are to be regarded as scarcely anything more than separate facts, which, for the purpose of giving a general view and rendering the classification more easy, I have intentionally selected from the organic chemical processes of vegetable life, which are constantly in operation, and with which we are as yet totally unacquainted. Almost all these materials con stantly exist together in the living plant, and it is merely their preponderance in a greater or lesser degree which enables us to say that the cell contains amylum or gum, and so forth. Only towards the termination of the individual life of the cells do we find them filled with a less number of different substances ; the cells which contain ethereal oil are probably the only instances in which we find but a single one.