156 Prof. Mayer's Observations on the 



progress of the temperature of the apartment, although artifi- 

 cial, was yet more or less in connexion with the motions of the 

 external temperature ; for the temperature of the apartment at- 

 tained its minimum between five and six in the morning, at the 

 moment when the stove was lighted ; it increased rapidly, until 

 two or three in the afternoon, and then gradually fell back to its 

 minimum. 



To measure the growth of the plants, the author made use of 

 a Paris foot divided into inches, lines, and quarter lines. This 

 instrument was furnished with a sufficiently broad base to let it 

 be placed upon the earth in the pots, as near as possible to the 

 plants, and always in the same place. The plants were con- 

 stantly plaeed and measured in the same order, and at the same 

 hours. The author having always measured to the summit of 

 each plant, has necessarily comprised in his appreciations of 

 growth, organs of different knots in various degrees of develop- 

 ment. The cotyledon, or first leaf of the gramineas, rises from 

 the ground to the height of about an inch before the second leaf 

 can be perceived, which rises from the former by the first leaf. 

 Thus he began with measuring up to the point of the Jirst leaf 

 or cotyledon ; then, when the second was visible, to the point of 

 this second leaf, and lastly to the point of the third. The in- 

 ternode of the first leaf had ceased to grow, the internode of the 

 second was still growing, and the third was only beginning to 

 shoot. 



The wheat plants a, b, c, of the vessel No. 1, and the barley 

 plants^, h, i, of the vessel No. 3., had their cotyledon almost 

 entirely developed, when they began to be measured. The 

 plants of the vessels Nos. 2. and 4., on the contrary, scarcely 

 shewed themselves above ground, and their second leaf did not 

 become visible until the 13th, although the seeds had been sown 

 on the 7th. On the 16th, in the morning, the third leaves of the 

 three plants of wheat of the vessel No. 1., and of the two barley 

 plants of the vessel No. 4. (the third having perished) had at- 

 tained nearly the third of the limb of the second leaf, which 

 continued to grow, while the third leaf of the barley plants of 

 the vessel No. 3. had already attained the half of the limb of 

 the second leaf ; lastly, the three plants of the vessel No. 2. had 

 not yet shewn their third leaf. 



