84 ROBERT A. BUDIXGTON. 



there is another large world of protoplasm identified with the 

 plant kingdom; and the question arises, "Is all protoplasm 

 enough alike so that that of plant associations, although of 

 course never normally exposed to thyroid influences, is, never- 

 the-less, susceptible to them?" If so, then the interest which 

 attaches to the physiological effect of this endocrine substance is 

 much increased; if not, then one of the differences in their 

 characteristics, which perhaps was instituted when animal and 

 plant protoplasms began their long evolutionary divergence, is 

 made roughly apparent. 



A further question which arises is: "Are animal and plant 

 protoplasms sufficiently alike so that, if both are susceptible to 

 thyroid materials, they both react in the same manner?" That 

 they apparently do to some infections has been fascinatingly 

 brought out by the investigations of Smith ('20) in his scholarly 

 studies into the nature of crown gall in plants, and its close 

 similarity, etiologically, to human cancer. Very numerous 

 instances of similar or comparable responses of plants and 

 animals to the same physical stimuli could be cited. 



The fact which has been taken as a point of departure in the 

 present study is the use of thyroid tissues or extracts in hastening 

 differentiation of vertebrate larval cell-masses into adult-like 

 organs, and the provoking of a general precocious metamorphosis. 

 The query, then, is: "Can thyroid gland materials cause pre- 

 cocious differentiation of unspecialized plant tissues?" 



EXPERIMENTAL METHODS AND RESULTS. 



The observations here described were made entirely on roots 

 growing from bulbs of Narcissus. Naturally, selection of a root 

 must be made with reference to the special tissue structure it may 

 exhibit. In some forms there is a clear-cut separation between 

 the root-cap and its adjacent tissues; in such cases the cap may 

 be cleanly removed from the adjoining tissues, there being no 

 derivational dependence between them. In other roots the 

 cap-cells are continuous with those of the root proper, a "common 

 initial zone" existing between them, from which zone cells bud 

 off into both adjoining areas. It is to this second type, "Type 5" 

 of Haberlandt ('14), that Narcissus belongs; as a convenient 

 reminder of the circumstances, a plan of its root tissue arrange- 



