PERIODICAL OPENING AND CLOSING OF FLOWERS. 11 



The limits of the mean expansion, excepting Pyrethrum corym- 

 bosum, are 5° and 67°. 



As regards the maximum : — 



Maximum iu Crocus vera us . . . . = 31 — 40 



.„ 4 species = 41 — 50 



10 „ = 51—60 



14 „ = 61—70 



15 „ = 71—80 



16 „ = 81—90 



13 „ = 91 — 100 



„ 4 „ =101—110 



8 „ =111 — 120 



Borkhausia fcetida . . = 121 — 130 

 „ Solauum vulgare . . = 131 — 140 



„ Scorzonera hispanica . =141 — 150 



„ Tigridia pavonia . . = 180 



„ Pyrethrum corymbosum = 190 



The same proportions hold good as with respect to the mean 

 expansion. The number of species increases as the phase 

 approaches 100 (90°), and then decreases. The usual limits of 

 the maximum lie between 30 and 130. 



With reference to the whole amount of expansion, or difference 

 between the maximum and minimum, the case is much the same 

 as with the maximum. The number of species increases when 

 the variation amounts to 75, and decreases when it exceeds 

 that measure. The limits of the diurnal change lie between 25 

 and 130, corresponding to angles of 22° and 112°. 



2. Dependence of the degree of expansion on temperature. — 

 We have seen that the time of sleep, as well with regard to its 

 duration as to the period at which it begins or ceases, is in close 

 connexion with the apparent daily course of the sun. This is not 

 the case with the degree of expansion, inasmuch as the temperature 

 of the air and other cosmical conditions are important agents in 

 the matter, as is evident on theoretic grounds : for the influence 

 of the sun's rays (insolation) on plants is greatly modified by 

 meteoric conditions, though the duration of the sun's influence is 

 always the same, at the same time of the year, as its apparent 

 diurnal course. The following table shows the temperature at 

 which the flowers of different species begin to expand. Since 

 the time of the year seems to influence the temperature at which 

 plants wake from their sleep, the mean epoch of observation for 

 every group is reckoned from the time appended in the tables to 

 each individual species : — 



