May i, 1884 



NA TURE 



In Nature (vol. xxix. p. 596) there is a letter signed James 

 Graves, in which lie says, " as to the magpie or any other bird 

 being able to fix dates exactly to the day, it is unproved and in- 

 credible. " I do not know what may be the case in regard to 

 birds-nestbuilding, but I can give two instances of the regularity 

 with which birds arrive at certain localities en route northward, 

 whatever may be the state of the weather. During a ten years' 

 residence on the shores of Hudson's Bay, the first Canada goose 

 of the spring migration was seen and generally shot on April 23. 

 At Toronto on Lake Ontario, large flocks of a pretty little plover 

 called the " black-heart," from a black patch on its breast, pass 

 along the islands, flying northward, on St. George's Day 

 (April 23), and are seldom or never seen even a day before or a 

 day after that date. The poor little birds have a sad time of it 

 for six or eight hours, as a number of sportsmen go out for the 

 occasion and knock them down by the half-dozen or more at 

 every shot. In this case, as in the other, wind and weather 

 appear to cause no difference John Rae 



4, Addison Gardens, April 25 



THE ABSORPTION OF WATER BY PLANTS 



AN ingenious instrument has lately been described by 

 Dr. J. W. Moll (Archives Neeilandaises, i. xviii.) 

 under the name of the Potometer. It is a modification 

 of Sachs' apparatus for determining the amount of water 

 which a cut branch absorbs in a given time. I have been 

 for some years in the habit of using a form of Sachs' 

 instrument, differing in principle from Moll's apparatus. 

 but resembling it in being especially adapted for making 

 observations at short intervals of time. As the subject 

 of transmission of water through wood is now attracting 

 attention among physiologists, it seems worth while to 

 describe my instrument. 



A short piece of thick indiarubber tube is slipped over 

 the cut end of a branch and firmly attached to it by wire 

 ties ; the other end of the rubber tube being securely fitted 

 to a glass tube which is filled with water. The other end 

 of the glass tube is closed by an indiarubber cork through 

 which passes a coarse thermometer tube. The apparatus 

 is now fixed so that the free end of the thermometer tube 

 dips into water. As the leaves evaporate the water in 

 the glass tube is sucked up by the cut end of the branch, 

 the loss being constantly made up by a current flowing in 

 through the thermometer tube. If then we can estimate 

 the rate of this current we shall know the rate of absorp- 

 tion of water. This is very simply done by allowing, for 

 a few seconds, the thermometer tube to suck in air instead 

 of water ; when a column of air a few millimetres in 

 length has been drawn in, the end of the tube is again 

 immersed in water, and the bubble travels rapidly along 

 the thermometer tube, when its speed is measured by 

 means of a chronograph. 



This method appears no doubt to be a rough one, and 

 is open to objections ; but I believe that it does not give 

 rise to serious errors, and it certainly demonstrates ex- 

 tremely well small changes in the rate of absorption 

 by a cut end of the branch. By means of my instrument 

 observations can be made at very short intervals ; for 

 instance, four readings were taken in 1' 50" ; it is there- 

 fore well adapted for observing rapid changes in the rate 

 of absorption. 



I reserve a full discussion of the merits and demerits of 

 the instrument for a later publication. 



Experiments, April 1884. — When a branch is first fitted 

 to the instrument the rate of absorption is extremely rapid, 

 owing to causes which need not here be considered, but 

 after a time the rate of absorption (which diminishes 

 with great rapidity) becomes constant. A branch of 

 Portugal laurel (Cerasus lusitanicd) was cut at 9 30 a.m., 

 and was not fitted to the apparatus until 10.15 am - 



The following table shows clearly the rapid decrease in 

 the rate of absorption :— l 



1 In this and the following tables I have not given the actual quantities of 

 waterabsirbed, merely the relative rates of absorption. 



Rate of Absorption 

 71 



53 

 40 

 26 

 25 

 25 



Sachs has called attention to the diminution in the 

 absorption which occurs when cut branches are placed in 

 water, and has shown that the absorbing power can be 

 renovated by cutting a fresh surface at the base of the 

 branch. This effect is well shown with my instrument. 1 



The above-mentioned branch of Portugal laurel which 

 had been placed in water at 9.30 a.m. gave a relative rate 

 of absorption of twenty-four at 12.28; at 12.30, between 

 6 and 7 cm. were cut off, and the branch was again fitted to 

 the machine, the operation lasting one and a half minutes. 



lime p in. Kate of 



h m Absorption 



12 28 24 



30 ... ... ... ■•■ fresh surface cut 



31A ... ... ... branch replaced 



33 35 



35 3° 



39 2 f 



45 2 ° 



54 26 



When the rate of absorption has become constant, 

 any variation in dampness or dryness of the air causes 

 variations in the transpiration of the leaves, and therefore 

 in the rate of absorption. These changes are well shown 

 by my instrument. The following experiment, made 

 with a branch of Portugal laurel shows the amount anrj 

 rapidity of the increase in absorption caused by exposing 

 the leaves to the sun shining through window-glass : — 



Time a m h m. Rate of Absorption 



14 



14 



14 



15 



15 



14 



Blind drawn up 



14 



10 44 

 49 

 55 



11 o 

 5 

 64 



7i> 

 9 ■ 



I2i 27 



Thus in six minutes the rate of absorption had nearly 

 doubled. A similarly rapid effect is seen when the sun- 

 light is cut off, when the rate of absorption falls. 



Time h in. Rate of Absorption 



12 5 33 



32 



blind down 

 27 



IOrt 

 I2| 



192 



25 



29 



That is, the rate of absorption diminished in the proportion 

 of 100 : 56 in twenty-four minutes, when the sunlight was 

 cut off. In the same way the effect of opening a window 

 and thus increasing the evaporation for the leaves, is a 

 once visible in increased rate of movement in the bubble. 



Cut Stem of Ivy 



Time a.m. Rate of 



h m. s. Absorption 



10 33 O 32 



11 o o 3 1 



window and door opened 



34 



37 



37 



33 



... window and door shut 



21 30 3 1 



22 30 29 



40 31 



ed not here Le discu^ed_whether the particular phenomenon her 

 is the same »s that described by Sachs. 



