Evidence from Somatic Histogenesis 59 



row cells, thus giving much more strength to the stem." 20 

 And the author goes into considerable detail in discussing 

 the presence and the absence of "wood tracheids," "scalari- 

 form pittings," "border pits," "spirally thickened walls" 

 and "sieve tubes" in the genera Zamia, Cordaites, Stangeria 

 and Cycas. 



That this well-nigh endless variety of character of the cell- 

 wall in adult plant tissues is due to the activity of the cell 

 protoplasm appears never to be questioned by botanists 

 so long as they are dealing with the actual structure and 

 development of the wall. "The cell-membrane is produced 

 by the protoplasm," we read in the section on morphology 

 in the Lehrbuch der Botanik by Strasburger, Jost, Schenck 

 and Karsten (llth German edition) this section being from 

 the pen of Strasburger himself. This simple, unqualified 

 statement of fact by Strasburger is the more noteworthy 

 because, as we saw in another connection, he has been one 

 of the extremists on the chromosome dogma of heredity. 

 Reading his statement that the cell-membrane is produced 

 by the protoplasm, with the indubitable fact in mind that 

 this membrane presents innumerable characters which are 

 taxonomically definitive, and hence are hereditary according 

 to the best criteria we have of hereditary characters, it 

 seems impossible to avoid seeing that it implies an irrec- 

 oncilable contradiction of Strasburger's often-repeated 

 view that the chromosomes are the sole bearers of heredity. 



To round out the primarily factual part of this discussion 

 two questions remain to be considered : first, that of heredity 

 in the main classes of tissues of multicellular organisms ; 

 and second, that of the results being reached by the latest 

 methods of cytoplasmic study on the behavior of different 

 portions of the cells in the histogenesis of these tissues. 

 What is implied in these two questions can be made clear by 

 a special case. Is the minute structure of striated muscle 

 tissue, for example, subject to heredity? If so, are the 



