56 The Unity of the Organism 



in form and size, but they are unlike in quality of rough- 

 ness. In Papaver orientate (52 a, b) and Papaver pilosum 

 (53 a, b,) the distal ends of the superficial cells project be- 

 yond the general surface of the trichome and turn out at 

 a rather acute angle. In Papaver soTnniferum, however, 

 these cells did not extend beyond the general surface, with 

 the effect that the trichomes of this species are smooth (fig- 

 ure 54 a, b)." ^^ 



This is especially instructive because the attribute in 

 question pertains to the shape and position of cells, and not 

 to differentiation within the cells. There, consequently, is 

 no room for even a reasonable surmise that the attribute is 

 explained by the chromatin instead of the cytoplasm. Even 

 though the account gives no information about the position 

 and behavior of the nuclei of the cells, it is hardly con- 

 ceivable that any one would maintain that the substance 

 itself of the cell-tips is not the main factor in the out- 

 turning of these tips characteristic of Papaver orientate 

 (figure 52 a, b). 



Dealing with quite another type of trichomes, those of 

 the walnut. Cannon writes: "A character which easily dis- 

 tinguishes the short secreting trichomes of Jwgtans cati- 

 fornica from those of Jugtans regia or Jugtans nigra 

 is the length of the head-cells." ^'^ Both drawings and tables 

 of measurements of the heads showing lengths and diameters 

 are given to bring out the positiveness of the distinction. 

 Furthermore, details of cell division and cell structure dur- 

 ing the development of the trichomes are furnished ; so the 

 visibte evidence that the cytoplasm is "inheritance material" 

 in this case is beyond question. What the invisible evidence 

 may be remains for further investigation to discover, but of 

 one thing we may be sure: no matter how many facts of 

 development now invisible may later become visible they will 

 not destroy the validity of the present visible evidence. 



How far it would be possible to go on pointing out specific 



