106 M. Dutrochet on the Temperature of Vegetables.' 



together, so that the soldering occupies the point of the angle, 

 the tAA'o sides of Avhich, the iron and copper, are almost in 

 juxtaposition, and separated only by a layer of varnish, which 

 covers all this part of the needles. The soldered point is 

 thrust also to the same depth of five millimetres into the part 

 of the vegetable submitted to observation. 



I will present here some modifications and additions to my 

 observations of last year, already explained. 



The heat of the green parts of vegetables, a heat the maxi- 

 mum of which I have stated to be ^ of a centesimal degree, is 

 sometimes elevated to |^ of a degree. This I have observed 

 in the stem of the Euphorbia lathyris. Stems discover a pe- 

 culiar or proper heat only in their herbaceous state ; they lose 

 it on becoming ligneous, or at least it is not then appreciable. 

 I have ascertained the existence of vegetable heat not only in 

 the pai'ts I have mentioned in my note of last yeai% but also 

 in roots, in fruits, and even the seminal embryos. It is easily 

 observed in the large cotyledons of the bean {Vicia fabd). 

 while they are stiU green. I have observed it also in mush- 

 rooms. Flower-buds discover a peculiar heat only when the 

 soldered point is placed in the ovai'y. When it is placed in 

 numerous petals folded back and pressed together, as hapj^ens 

 in the flower-buds of the hundred-leaved rose, or the double 

 peony, no indication of heat is observed. The peculiar heat 

 of young stems, which often disappears during the night, some- 

 times continues during this period, but it then experiences a 

 remai'kable diminution. It is usually in the course of three 

 hom'S after mid-day that vegetable heat is at its maximum. 

 This is the period of the day when ordinarily, but not always, 

 the heat and light are greatest. Beyond the invariable hour 

 at which the maxinuun of the peculiar heat of each plant 

 takes place, this heat goes on diminishing, althovigh the ex- 

 ternal heat and light may then augment in intensity. This 

 diurnal paroxysm, this sort of quotidian fever, which green 

 vegetables experience, presents no interruption, except during 

 the complete absence of the diurnal light ; and, what is very 

 remarkable, this interruption of the paroxysm does not always 

 happen on the first day of total obscurity. I have seen this 

 paroxysm return on the first, and even sometimes on the se- 

 cond day of dai-kness, and its maxiinum always happeped at 



