ORGANIC FORM AND ARCHITECTURE 701 



THE CELL 



THE CELL THEORY.— As we have seen, not a few of the early 



microscopists made attempts to define the minute elementary parts 

 that build up Uving creatures; but it was not till 1838 that the idea 

 of the cell as a structural and functional unit was clearly focused 

 in the Cell-Theory or, better, Cell-Doctrine (Zellenlehre) of Schwann 

 and Schleiden. Its three propositions may be recalled. First, there 

 is the morphological statement, that all living creatures have a 

 cellular structure, and that all but the simplest, that is to say all 

 that have what may be called a "body", are built up of cells and 

 modifications of cells. Second, the Cell-Theory includes the physio- 

 logical statement, that the activity of a many-celled organism is 

 the sum of the activities of the componentc ells. This idea requires 

 to be safeguarded by the fact of correlation, for the life of the whole 

 cannot be described without recognising that it is more than the 

 life of all its parts, just as the behaviour of a group of men with 

 a common purpose cannot be adequately described merely in 

 terms of the movements of the individuals. Third, the Cell-Theory 

 includes the embryological statement, that the individual many- 

 celled organism begins its hfe, in all ordinary cases, as a fertihsed 

 egg-cell, which divides and re-divides to form an embryo. In other 

 words, developing and growing imply cell-division. Cellular structure 

 is a condition of differentiation. 



But after the formulation of the Cell-Doctrine, it gradually became 

 evident that the structure of the unit was complex to an unforeseen 

 and extraordinary degree, just as the atom has slowly revealed the 

 complexity of its organisation in modern physics. The main con- 

 clusions of Schwann and Schleiden remain true to-day, but the 

 picture of the cell has become much more intricate. 



Convenient objects for examination are easily found, as even by 

 tearing a strip of epidermis from a leaf, say conveniently a garden 

 iris or other free-growing monocotyledon, and then other leaves of 

 various kinds. Endless sources of interest can be established from a 

 single country walk, by taking out a few wide-mouthed bottles, 

 and bringing home in each a sample of weed and water and bottom 

 taken from the different pools and ditches on the way, for each 

 will be found a source of varied wonders well worth searchings, and 

 these repeated for weeks and months on end. With such a growing 

 range of aquaria on the window-sill or microscope- table, one has 

 an unending range of observation and of interest, in repeating for 

 oneself the centuries-long record of such discovery. From this 

 knowledge of Protozoa and Protophytes and various Bacteria, of 

 filamentous Algae and so on, it is easy to go further, as especially 

 by the sea-shore. Thus the egg-cells of sea-urchins or starfishes are 



