DEPARTMENT OF BOTANICAL RESEARCH. 67 



The Behavior of Protoplasm as a Colloidal Complex: Factors affecting the 

 Growth of Protoplasm, by Francis E. Lloyd. 



It has already been shown that the protoplast in many kinds of 

 pollen contains no sap-vacuoles of optically demonstrable size. The 

 evidence offered indicates that the water taken up when the pollen 

 is placed in contact with it is solely imbibed, and that the earlier 

 growth-period of the pollen-tube results in chief part from imbibition 

 pressure and not from turgor. That osmotic pressure during this 

 period is absent or negligible in quantity (as compared with imbibi- 

 tion pressure, optical evidence aside) is inferred from the fact that 

 growth may take place against a surrounding medium of very high 

 concentration (50 per cent cane sugar), and the protoplasm may even 

 burst, preventing, by rupturing the sustaining cellulose wall, the nor- 

 mal attainment of size which might otherwise be possible. 



Proceeding from the above inference, it has been sought to deter- 

 mine quantitatively what the imbibition pressure of growing pollen 

 protoplasts might be, as well as the effect of the presence of electro- 

 lytes upon growth-rates. Pollen of Lathyrus was found most useful. 



In distilled water the pollen may either burst very soon without 

 measurable growth or it may produce short tubes, in exceptional 

 instances only reaching a maximum length of about 100 microns in 2 

 hours. At or before this length of tube is attained it bursts at the 

 apex and the protoplast gushes forth, A portion may be retained and 

 live for some hours. In 10 per cent cane sugar the matter is little 

 better, giving a maximum length of 100 microns in 40 minutes, with 

 bursting at or before this time. A maximum growth-rate of 200 

 microns an hour and total growth of 640 microns were attained in 20 

 per cent cane sugar. At higher concentrations both growth-rate and 

 total growth were less, but were not totally inhibited even in a concen- 

 tration of 50 per cent. In 30 per cent the rate was about one-half 

 that in 20 per cent and in 40 per cent less than 0.1 (0.07). It thus 

 appeared that an outward pressure of the protoplast upon the cell- 

 wall in excess of a certain quantmn can not be used for effective 

 growth. To speak more specifically, and so far as we can see at the 

 moment, the rate at which the protoplast can build the cell-wall of the 

 pollen-tube is a limiting factor. The total range of pressures which 

 allow growth at a greater or lesser rate is, however, wide, as indicated 

 by the above-mentioned cane-sugar concentrations which permit growth. 



When the pollen-tubes have attained a length of 80 microns more 

 or less, vacuolization sets in, and we may no longer attribute to imbibi- 

 tion pressure the chief or, at length, even the greater role. Until this 

 inversion of role has taken place, however, the rates of growth of the 

 pollen-tubes may be regarded as a critical index of the effects of 

 swelling or shrinking of the protoplasm by electrolytes upon growth- 

 rates, since it has already been shown (Carnegie Institution Year Book 



