The Principles of biology v2 Author:Herbert Spencer Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER II. THE MORPHOLOGICAL COMPOSITION OF PLANTS. § 180. Evolution implies insensible modifications and gradual transitions, which render definition dif... more »ficult—which make it impossible to separate absolutely the phases of organization from one another. And this indefmiteness of distinction, to be expected a priori, we are compelled to recognize a posteriori, the moment we begin to group morphological phenomena into general propositions. Thus, on inquiring what is the morphological unit, whether of plants or of animals, we find that the facts refuse to be included in any rigid formula. The doctrine that all organisms are built up of cells, or that cells are the elements out of which every tissue is developed, is but approximately true. There are living forms of which cellular structure cannot be asserted; and in living forms that are for the most part cellular, there are nevertheless certain portions which are not produced by the metamorphosis of cells. Supposing that clay were the only material available for building, the proposition that all houses are built of bricks, would bear about the same relation to the truth? as does the proposition that all organisms are composed of cells. This generalization respecting houses would be open to two criticisms:—first, that certain houses of a primitive kind are formed, not of bricks, but out of unmoulded clay; and second, that though other houses consist mainly of bricks, yet their chimney-pots, drain-pipes, andridge-tiles, do not result from combination or metamorphosis of bricks, but are made directly out of the original clay. And of like natures are the criticisms which must be passed on the generalization, that cells are the morphological units of organisms. To continue the simile, the truth turns out to be, that the primitive ...« less