214 THE FORMS OF CELLS [ch. 



through all its successive phases of form is never in complete 

 equilibrium ; but is merely responding to constantly changing 

 conditions, by phases of partial, transitory, unstable and con- 

 ditional equilibrium. 



It is obvious that there are innumerable solitary plant-cells, 

 and unicellular organisms in general, which, like the yeast-cell, do 

 not correspond to any of the simple forms that may be generated 

 under the influence of simple and homogeneous surface-tension ; 

 and in many cases these forms, which we should expect to be 

 unstable and transitory, have become fixed and stable by reason 

 of the comparatively sudden or rapid solidification of the envelope. 

 This is the case, for instance, in many of the more complicated forms 

 of diatoms or of desmids, where we are dealing, in a less striking 

 but even more curious way than in the budding yeast-cell, not 

 with one simple act of formation, but with a complicated result 

 of successive stages of localised growth, interrupted by phases of 

 partial consolidation. The original cell has acquired or assumed 

 a certain form, and then, under altering conditions and new 

 distributions of energy, has thickened here or weakened there, 

 and has grown out or tended (as it were) to branch, at particular 

 points. We can often, or indeed generally, trace in each particular 

 stage of growth or at each particular temporary growing point, 

 the laws of surface tension manifesting themselves in what is 

 for the time being a fluid surface ; nay more, even in the adult 

 and completed structure^ we have little difficulty in tracing and 

 recognising (for instance in the outline of such a desmid as Euas- 

 trum) the rounded lobes that have successively grown or flowed 

 out from the original rounded and flattened cell. What we see in 

 a many chambered foraminifer, such as Globigerina or Rotalia, is 

 just the same thing, save that it is carried out in greater complete- 

 ness and perfection. The little organism as a whole is not a figure 

 of equilibrium or of minimal area ; but each new bud or separate 

 chamber is such a figure, conditioned by the forces of surface 

 tension, and superposed upon the complex aggregate of similar 

 bubbles after these latter have become consolidated one by one 

 into a rigid system. 



Let us now make some enquiry regarding the various forms 



