EFFECT OF THYROID GLAND ON PROTOPLASM. 85 



ment is shown in a diagram of its longitudinal section in Fig. i. 

 Neither the "common initial zone" nor the root-cap shows any 

 distinct differentiation ; they form an essentially parenchymatous 

 mass. In a proximal direction, however, differentiation is soon 

 met, i.e., the cylindrical periblem, and the centrally placed 

 plerome mass, also a cylinder. 



The real question, then, which is being applied to the Narcissus 

 root is: "Do the specialized tissues of the root proper extend 

 down further into the tip in such roots as are grown in nutritive 

 media containing thyroid constituents than they do in roots 

 grown in nutrient media alone?' 



re 



In., i. Showing diagraniniatically the arrangement of^tissues in the root-tip 

 <'t .V longitudinal section, c.i.z., common initial zone; p., periblem;* pi., 



pleruine; r.c., root cap. 



Several do/ens of Narcissus bulbs were rooted in bottles con- 

 taining i 20 cc. of Pfeffer's nutrient solution to which had been 

 added gland substance (Parke Davis and Co.'s dry thyroid 

 tablets) in these amounts: 2.5. grains, 5 grains, 7.5 grains, and 

 10 grain.-, respectively. It is well known, of course, that bulbs 

 differ much in their "strength," and that in consequence of 

 variation in vitality their root growth is not uniform in rate, 

 length and other features; but there is an easily observable 

 average which characterizes the normal or any experimental 



