A re-statement of the cell theory : with applications to the morphology, classification, and physiology of protists, plants, and animals : together with an hypothesis of cell-structure, and an hypothesis of contractility / by Patrick Geddes.

Date:
[1884]
Catalogue details

Licence: Public Domain Mark

Credit: A re-statement of the cell theory : with applications to the morphology, classification, and physiology of protists, plants, and animals : together with an hypothesis of cell-structure, and an hypothesis of contractility / by Patrick Geddes. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    22/32 (page 284)
    alike become stationary, and either dry up or encyst themselves. The cell-cycle in plants therefore is only found in its entirety in algaj. Archegoniates are indeed terrestrial, but their brief cell-cycle during fertilisation is absolutely dependent upon the abundant moisture, without access to which neither moss, liverwort, nor pro- thallium ever occurs. Thus it is that the higher terrestrial plants have become restricted to the encysted phase. Only to escape death, has the dryad become thus shut up within the tree; but once so protected the extensive replacement of the cryptogams by the phanerogams, in all the less humid climates of the world, is readily accounted for. Passing to animal life, the vast preponderance of aquatic forms over terrestrial, is very similarly to be accounted for by the aid of the present theory. Only the higher members of a few groups have successfully emerged from their native element, and their existence depends upon their differentiation of an internal fluid medium, of that milieu interieur upon which Claude Bernard was wont to lay such stress,* this in turn depending upon the early differentiation of in- ternal cavities. The interdependence of morphological and physio- logical theory will be sufficiently obvious from such considerations.! 14. Theory of Variation.—The more completely one accepts and reflects upon the theory of natural selection, the more one feels the necessity for some view more satisfactory than heretofore of the causes of variation. % The present conception of the cell-cycle seems to go far towards supplying this. On the ordinary conception of the cell theory, that of the plant as an aggregate of encysted cells, and of the animal as an aggregate of essentially amoeboid ones, the organism cannot be credited with any innate variability—its ob- served variations are merely those which it receives, so to speak, between hammer and anvil—from the forces of the environment. The present conception, however, of all cells, however varied and specialised, being essentially differentiations from an encysted, an amoeboid or a ciliated form, and of these forms as phases of a single form-history, enables us to credit the cells and the resultant organism with an innate tendency to variation, and this along * PMnomencs dc la vie communs aux an. et auxvig., Paris, 1879. + Morphology, Ency. Brit., 'Eel. of Morphol. to Physiol.' X Cf. Or igin of Species.