EFFECT OF THYROID GLAXD ON PROTOPLASM. 



8 9 



results of this study, as indicating precocious specialization, is 

 arbitrary as against other possible judgments. For example, 

 does not a long root of Narcissus normally possess a root-cap 

 thicker than that of a short root? To test this point, a series of 

 roots grov, n in nutrient solution alone were cut when at the same 

 or less length than those of the thyroid "fed" line, the question of 

 relative age being disregarded. On making measurements of 

 these it was found that the short normal root shows an extent of 

 root-cap equal to or even in excess of that of a longer normal root. 

 The question here at issue can be most easily met by offering the 

 following t. title of averages of root-cap length (tip to periblem 

 and pleroine) of thirty roots each, taken from long-normal 

 (control), short-normal, and thyroid "fed" groups: 



It is thu> plainly apparent that the cap of the experimental line 

 \\.i- inoie deeply invaded by the specialized tissue than were 

 either \ tin- check roots with which there was any reason for 

 rump. niii- it. 



One .I!M i naturally raises the question whether the results noted, 

 in-te.nl <>!' being those of accelerated differentiation, could not as 

 \\ell IK- (K i il>ed as simple abbreviation or inhibition of root-cap 

 growth. It is possible that such an interpretation would be 

 perfectly \.ilid; at the same time, one should reflect that the 

 t-t led is one, not on the root-cap alone, but on the entire root. 

 While the 1'oiv^oing measurements give information as to only 

 one feature, i.e., length of root-cap, other specifications are also 

 modified by the treatment: e.g., its entire length is less than that 

 of the normal; its average diameter is greater at nearly every 

 part of its growth ; it shows tendencies to localized swellings and 

 crookecliu->. Measurements of these other features of the 

 thyroid "fed" line, however, it is impossible to make in any 



