204 THE FORMS OF CELLS [ch. 



in his great work on so-called Fluid Crystals*, to which we shall 

 afterwards return, has shewn how, under certain circumstances, 

 surface-tension phenomena may coexist with crystallisation, and 

 produce a form of minimal potential which is a resultant of both : 

 the fact being that the bonds maintaining the crystalline arrange- 

 ment are now so much looser than in the solid condition that the 

 tendency to least total surface-area is capable of being satisfied. 

 Thus the phenomenon of "liquid crystallisation" does not destroy 

 the distinction between crystalline and colloidal forms, but gives 

 added unity and continuity to the whole series of phenomena f. 

 Lehmann has also demonstrated phenomena within the crystal, 

 known for instance as transcrystallisation, which shew us that we 

 must not speak unguardedly of the growth of crystals as limited 

 to deposition upon a surface, and Biitschli has already pointed out 

 the possible great importance to the biologist of the various 

 phenomena which Lehmann has described t. 



So far then, as growth goes on, unafltected by pressure or other 

 external force, the fluidity of protoplasm, its mobility internal 

 and external, and the manner in which particles move with 

 comparative freedom from place to place within, all manifestly 

 tend to the production of swelling, rounded surfaces, and to their 

 great predominance over plane surfaces in the contour of the 

 organism. These rounded contours will tend to be preserved, for 

 a while, in the case of naked protoplasm by its viscosity, and in 

 . the presence of a cell- wall by its very lack of fluidity. In a general 

 way, the presence of curved boundary surfaces will be especially 

 obvious in the unicellular organisms, and still more generally in 

 the external forms of all organisms ; and wherever mutual pressure 

 between adjacent cells, or other adjacent parts, has not come into 

 play to flatten the rounded surfaces into planes. 



But the rounded contours that are assumed and exhibited by 



* Lehmann, 0., Flussige Krysfalle, soivie Plasticitdt von Krystallen im allge- 

 meinen, etc., 264 pp. 39 plL, Leipsig, 1904. For a semi-popular, illustrated account, 

 see Tutton's Crystals (Int. Soi. Series), 1911. 



t As Graham said of an allied phenomenon (the so-called blood-crystals of 

 Funke), it "illustrates the maxim that in nature there are no abrupt transitions, 

 and that distinctions of class are never absolute." 



X Cf. Przibram, H., Kristall-analogien zur Entwickelungsmechanik der Organ- 

 ismen, Arch. f. Entw. Mech. xxii,p. 207, 1906 (with copious bibliography); Lehmann, 

 Scheinbar lebende Kristalle und MyeUnformen, ibid. xxAa, p. 483, 1908. 



