52 BOTANICAL GAZETTE [JANUARY 



AI! the plants used were young, in good growing condition, and in most 

 cases were taken just before flowering. It will at once occur to the reader 

 that in some cases conclusions have been drawn from too small a number 

 of plants, but since in these experiments the plants must be sacrificed 

 completely, it was impossible to obtain more than three of some species- 

 one for exudation and two for pressure. However, this does not involve 

 so great a possibility of error as it seems at first sight, for, although it is 

 possible that the plant used may be abnormal, the probabilities, according 

 to QuETELEx's law, are that it will fall near the mean. The temperature 

 of the laboratory during obser\'ation of the experiments was i8°-22°C. 

 The soil temperature at time of highest pressure was i7°-i8^C. 



The results obtained for quantity and pressure of exudation are given 

 in the following table, in which the first and fourth columns give the number 

 of plants used for exudation and for pressure experiments, respectively. 



From the table on page 53 it will be seen that the plants giving the highest 

 mean pressures, in order of amount, are Salvia involucrata, Helianthus 

 annuiis, Fuchsia speciosa, with others following according to the table. 

 When considered in order of maximum pressures, the highest are given by 

 Fvchsia speciosa, Salvia involucrata, and Lycopersicum esculentum. The 



1*1 « « 



Senecio 



Salvia 



For the practical purpose of demonstration, taking into consideration 

 high pressures, ease of manipulation, and abundance of plants, the very 

 best are Fuchsia speciosa, Chrysanthemum jndescens, and Pelargonium 

 mnaU, Since they have stout, woody stems, there is no danger of compress- 

 mg the vessels in making a tight joint with the pressure gauge. With the 

 pressure gauge attached they maintain a high pressure for about a week, 

 usually giving the highest pressure between 10 and 12 o^clock on the second 

 day. The next best are Heliotropium peruvianum. Pelargonium peliatum, 

 and AbutiloH. These give lower pressures than the preceding, but they 

 have a slight advantage in another way. The stems of vigorous young 

 plants have about the same diameter as the manometer tubing and there- 

 fore can be more readUy attached to the gauge. Other plants which 

 ^e high pressures are Lycopersicum escdentum and Fkaseolus vulgaris. 

 These have somewhat soft stems, though with care it is not difficult to 

 attach the gau^. 



The foUowing plants cannot be used advantageously for this experi- 

 ment: Euphorbia ptdcherrinia, because of its latex which thickens and 

 closes the ducts in a very short time; Ricinus communis, because of its 

 holkm ^m; Senecio tmkanioides and Tropaeolum majus, because their 



