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substances on account of some similarity of structure, even 

 if that similarity is far from that presented by isomor- 

 plious crystals. 



The biologists have tried to inoculate tissues or other 

 biological materials by touching them with ice crystals. 

 In general, the method is described as successful although, 

 here and there, some authors express a doubt as to its 

 efficacy. 



Several plant physiologists used, for inoculating tissues 

 or organs such as leaves, a method which consisted in put- 

 ting a drop of water at the surface of the material, with 

 the idea that water would freeze first and seed the adja- 

 cent tissue. Others who wanted to prevent crystallization, 

 took precautions against any moisture on the surface. 



Mtiller-Thurgau (1881) claims that potatoes cut into 

 pieces subcool less than intact potatoes, because of the 

 easier formation of centers on the cut surfaces. 



According to Mez (1905), when a tissue was in contact, 

 at one point, with the wall of a cold glass container, in- 

 stead of being isolated from it by air, subcooling did not 

 occur because of seeding by the ice formed at the cooler 

 point. This author went so far as to say that he could 

 guarantee a strong subcooling if a plant tissue was cooled 

 in oil (he used castor oil) while there was no or little 

 subcooling if the tissue was cooled in water. 



Voigtlander (1909), to obtain subcooling in plant tissues, 

 removed with absolute alcohol all traces of moisture on 

 the glassware to come in contact with the tissues and on 

 the thermo-needle to be inserted in them. 



Harvey (1919), for preventing seeding by the extruded 

 sap on the cut surfaces of leaves and petioles, dried them 

 and covered them with vaseline. He also reported that 

 leaves, stems and petioles covered with wax, bloom, or a 

 thick mat of epidermal hair can be subcooled to lower tem- 

 peratures than organs not so protected, or than plants in 

 which the coverings were removed or broken. Such a 

 protection is attributed to a prevention of seeding. A 

 drop of water laid on the heavily covered samples did not 

 seed the tissue below, as it did in cases of nude epidermis. 



