On the "Blaze Currents " of the Frog's Eyeball. 439 



threads points to their value as a means of conducting food material to 

 the developing cork. 



In the phloem there is a sharp contrast between the starch-containing 

 medullary ray cells and bast parenchyma on the one hand, and the 

 sieve tubes on the other, and no threads can be found directly con- 

 necting the parenchymatous cells with the sieve tubes, but the albu- 

 minous cells of the ray possess numerous thread groups which com- 

 municate with both tissues. The starch medullary ray cells in the 

 phloem and xylem possess numerous threads in the tangential and 

 basal walls, especially in the former, and are also united with the bast 

 parenchyma and albuminous cells. 



The sieve tube threads which occur only in the radial walls always 

 show a median dot. 



The existence of threads in the xylem is doubtful. All living 

 parenchymatous cells show them, but it seems probable that they 

 quickly disappear when the cells become lignified. In the case of 

 young bordered pits there is softie evidence that the torus is traversed 

 by connecting threads which are soon obliterated. 



The leaf of Pinus sylvestris shows a distribution of connecting threads 

 similar to that noticed in the cotyledon. The endodermis is seen to be 

 an important layer connecting the tissues of the stele with those of 

 the cortex by means of thread groups in the tangential walls. In the 

 pericycle there are both dead and living cells, but no threads persist 

 in the walls connecting the dead with the living cells. 



The albuminous cell thread groups are very well developed, and their 

 function and peculiar properties are discussed. 



In conclusion, the general distribution of the connecting threads 

 throughout the tissues is considered. 



" On the ' Blaze Currents ' of the Frog's Eyeball." By A. D. 

 WALLER, M.D., F.R.S. Received December 6, Read Decem- 

 ber 6, 1900. 



(Abstract.) 



The normal electrical response to light is positive. The normal 

 electrical response to every kind of stimulus is positive. The normal 

 response of the frog's eyeball is partly retinal, partly by other tissues. 

 The direction of response is reversed by pressure. 



The normal " blaze currents " excited by single induction shocks, 

 and by condenser discharges, are comparable with the normal dis- 

 charges of an electrical organ. Their maximum voltage is of the 

 same order as that of the discharge of a single electrical disc (over 



