342 THOMAS J. HELDT 



other, most delicately interrelated and adjusted, specialized and 

 differentiated, if such terms are permissible in this connection, 

 to a high degree. There is however the one common element, 

 water, whose proportional presence depends on the various con- 

 ditions to which the tissue may be heir. If now this complex 

 aggregate be subjected to a freezing temperature, there is, as 

 is already evident from previous statements, a separation of 

 water. This separation of water is strikingly dependent on the 

 factors before noted. If the freezing is slow the water as a rule 

 collects in the interstices of the tissue and thus in the subsequent 

 ice formation there are comparatively few centers of crystalliza- 

 tion. If however, the freezing is rapid the rapidity of the proc- 

 ess does not permit the water to collect in a few, apparently the 

 least resistant, interstices but forces it to crystallize in numerous 

 places. It would seem that in the employment of low temper- 

 atures, the more .rapid the reduction the more numerous the 

 centers of crystallization, Liesegang states that if the reduction 

 in temperature be great enough the centers of crystallization 

 become so numerous as to warrant the designation colloidal ice, 

 the existence of which has been proven by Ostwald and Weimarn 

 (cited by Liesegang). 



Since it is in the more slowly frozen tissue that the more 

 typical reticular structure occurs, we must return to that con- 

 dition. Just how and why the water of the various tissue ele- 

 ments collects in the interstices of the tissue during the process 

 of freezing is explained in considerable detail, in the case of 

 plant tissue, by Wiegand ('06 b). Just what, at a freezing tem- 

 perature, determines the formation and location of a center of 

 ice crystallization Wiegand does not state. Manj^ factors no 

 doubt are involved, the more important ones however are prob- 

 ably the following: the minimal amount of solute present in the 

 water, and the relative molecular capillarity with which this 

 water is held, together with the molecular distribution and ar- 

 rangement, at that particular instant and position. With the 

 formation of the ice crystals of course comes the molecular force 

 of cr3^stallization which continues to abstract water from the 

 particular tissue element in question with a simultaneous increase 



