INFLUENCE OF DUCTLESS GLAND ON PLANT TISSUES. 



DISCUSSION. 



The almost constant effect of abnormal amounts of thyroid 

 tissues or extracts in the food or environment (or both) of 

 developing animals has been to accelerate differentiation in 

 premature ways. So too, one may interpret increased fission 

 rate in Protozoa as indicating a similar effect, fission being a 

 procedure characteristic of their attainment of adult physiological 

 conditions. Such precocious metamorphosis of amphibian and 

 insect larvae is naturally coincident with small size. 



The difficulties in estimating the effect of substances on plant 

 tissues in terms of animal response and metabolism are obvious, 

 and one should perhaps heistate to make any comparisons. 

 However, all protoplasm obtains its raw materials through its 

 permeable cell walls; and one may also go further and say that 

 the root tips of bulbs, as they begin to grow, represent a kind of 

 embryonic tissue with a minimum of specialization. In brief, 

 the effect of thyroid substances on-onion root-tips is to retard, or 

 partially inhibit, size-growth; and this seems precisely the effect 

 on embryonic animal tissue. In the latter, a hastening of physio- 

 logic and morphologic differentiation is also present; if the same 

 be true in these root-tips, it naturally cannot be judged from 

 external appearances, though one cannot deny that premature 

 differentiation may be present. It is hoped to report on this 

 point in a later communication. 



Since the work of Marine and Lenhart, Morse, Swingle and 

 others has made certain the earlier assumption that iodine is the 

 most active principle in thyroid stuffs, a series of experiments in 

 which only iodine was added to the nutrient solution was carried 

 out. To make more significant and exact the comparison be- 

 tween such an experiment and those in which dessicated gland 

 was used, KI was added in amounts based upon the accepted 

 estimate that o.oi c.c. of a saturated solution of KI furnishes 

 the amount of iodine present in one grain of thyroid. Onion 

 root-tips, sprouting in media with this iodine content showed no 

 growth-rate which was specifically different from that of controls 

 growing in nutrient solution alone. 



Further sets of experiments were carried out with pituitary 

 gland tablets, using strengths of 2, 1.5, I and 0.5 grains in 120 c.c. 



