INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 109 



It is sometimes necessary to study both faces of a section. It 

 must then be turned over — an operation which can be performed 

 without diiBculty after a little practice. For this purpose M. Vesque 

 uses a cutting needle. When it is known beforehand that this will 

 be required, the section may be placed between two pieces of thin 

 glass, and can then be easily tm*ned as often as required. 



Metastasis of Germination at various Temperatures.* — A series 

 of experiments on the changes which take place during the germina- 

 tion of peas has led W. Detmer to the following conclusions : — 



When the seeds attain the same stage of deveh^pment or germina- 

 tion at ditferent temperatures, the same amount of dry substance is 

 consumed ; and as germination advances, the loss of dry substance 

 increases ; a larger amount of dry substance is lost in the same time 

 at a higher than at a lower temperature. A comparison of the 

 chemical composition of the seedlings grown at different temperatures 

 with that of the seeds shows that the jirocesses of metastasis proceed 

 in the same way during germination when the seedlings undergo the 

 same loss of dry substance, i. e. reach the same stage of development 

 at ditferent temperatures. One hundred seeds, whether they had 

 germinated for ninety-four hours at 23^ C, or for one hundred and 

 thirty-eight hours at 19^ C, had lost almost precisely the same 

 amount of dried substance, i. e. had attained the same stage of 

 development ; and the amount of starch and dextrin that had dis- 

 appeared was found to be the same in each case. 



Action of Low Temperatures on the Germination of Seeds.t 



Experiments on the influence of temjierature on germination were 



first attempted in 1832, by MM. Edwards and Colin. The reduction 

 of temperature was effected by the evaporation of svilphuric acid hi 

 vacuo. Seeds submitted for fifteen minutes to the low temperature of 

 — 40° C. were totally unharmed. In 1860 the question was again 

 taken up by Professor Wartmann, and with tiie same result; the 

 seeds experimented on were reduced to the still lower temperature 

 of -110= C. 



The experiments of MM. 0. de Caudolle and Raoul Pictet (details 

 of which arc now given) were made on Lepidium sativum, Sinapia 

 alba, Brassica oleracca, and Triticum vuhjare. 



Seeds of each of these species were (27th Marcli) placed in thin 

 glass tubes, and enclosed, together with a thermometer, in a test-tube, 

 which was liermetically sealed and swatlied in tow. By keeping the 

 tow constantly wet with sul[)huric acid, the temperature was gradually 

 reduced. At 4.25 p.m. it was — 3',)°C. ; at 5.0, — 43 ; at G.O, 

 -47"; at 7.0, —49°; and at 8.0 to 10.0 it was maintained at —50°. 

 The next day but one, twenty-four of each of the seeds were planted 

 ab)nf with others of the same species, and from the same croj), but 

 which had not been frozen. On 23rd April all the seeds of three out 

 of the foiir species had germinated, no difference whatever being 



♦ ' Forricbuiigen aus dcin Gcb. dcr Agriculturiihybik,' ii. p. 282; soe ' Nutur- 

 forwher,' xii. (lH7i») i). :!7G. 



t 'Arch. yd. riiyH. ct Nut.,' ii. (IST'-O i>. O^'.t. 



