EXPERIMENTAL MORPHOGENESIS 91 



from understanding the whole as ever. All means of 

 morphogenesis are only to be considered as the most general 

 frame of events within which morphogenesis occurs. 



Some Remarks on the Importance of Surface Tension in 

 Morphogenesis. There are a few purely physical phenomena 

 which have a special importance in organic morphology, all 

 of them connected with capillarity or surface tension. Soap- 

 lather is a very familiar thing to all of you : you know that 

 the soap-solution is arranged here in very thin planes separated 

 by spaces containing air : it was first proved by Berth old 1 

 that the arrangement of cells in organic tissues follows the 

 same type as does the arrangement of the single bubbles of 

 a soap-lather, and Biitschli 2 added to this the discovery that 

 the minute structure of the protoplasm itself is that of a 

 foam also. Of course it is not one fluid and one gas which 

 make up the constituents of the structure in the organisms, 

 as is the case in the well-known inorganic foams, but two 

 fluids, which do not mix with one another. One general 

 law holds for all arrangements of this kind : the so-called 

 law of least surfaces, expressed by the words that the 

 sum of all surfaces existing is a minimum ; and it again 

 is a consequence of this law, if discussed mathematically, 

 that four lines will always meet in one point and three 

 planes in one line. This feature, together with a certain 

 law about the relation of the angles meeting in one line 

 to the size of the bubbles, is realised most clearly in 

 many structures of organic tissues, and makes it highly 

 probable, at least in some cases, that capillarity is at work 

 here. In other cases, as for instance in many plants, a 



1 Studien ilber Protoplasmamechanik, Leipzig, 1886. 

 ' Unters. ub. mikroskopische Schaume und das Protoplasma, Leipzig, 1892. 



