USE OF THE SPECTEO SCOPE IN STUDY OF PLANT LIFE. 89 



The next method I adopted was to take small plants with their 

 roots carefally lifted and freed from soil, and to insert them in test- 

 tubes as before. The results were even more unsatisfactory than with 

 cut specimens, for, excepting Eadish (the thick root of which pre- 

 sumably acts as a reservoir of water), the others, having fibrous roots, 

 gave a steadily decreasing loss day by day, showing no maximum or 

 minimum, except in some cases with clear glass on the sixth day, on 

 which the loss was greater than on the preceding. 



One suspects, therefore, that roots naturally grown in soil and 

 transferred to water, cannot carry on their function of absorption in a 

 normal manner beyond a very short period of time. My experience 

 seems to corroborate that of Sacks'^, quoted by DucHAETEEf : — " Ce 

 physiologiste a reconnu que les racines qui se sont produites dans la 

 terre ne peuvent vegeter ensuite dans I'eau et que reciproquement celles 

 qui ont pris naissance dans I'eau ne peuvent remplir leurs fonctions 

 dans la terre. " 



The plan I finally adopted was to grow small plants in miniature 

 pots, two inches high and nearly two inches in diameter. These can 

 be entirely wrapped up in gutta-percha sheeting, which is carefully 

 bound round the stem of the plant with cotton-wool within and around 

 the stem. This effectually prevents any evaporation from the surface 

 of the earth or pot; and all loss of weight is due to the transpiration 

 from the exposed surface of the plant alone];. 



My experiments were made upon lettuce, box, Echeveria, small 

 seedling palms, ferns, cacti, and many other kinds of shrubs and 

 herbs ; having selected them with very various degrees of density in 

 the epidermis, as well as of different families. The results would seem 

 to entirely corroborate the conclusion of Wiesnee, that transpiration is 

 mainly effected by the Eed, Blue, and Vioiet rays ; while the (optically) 

 brightest rays of yellow and green are generally less able to effect it, 

 even if they do not hinder it. I emphasise this sentence, as there 

 appear to me to be grounds for coming to such a conclusion. 



Desceiption of Expeeiments. — The experiments were all con- 

 ducted in a room with one window of north aspect, into which the sun 

 never entered, except just before setting in midsummer, and then only 

 at one corner of the windov\^. The light was, moreover, partially 

 obscured by foliage of high trees in front of it. The window was 

 never opened, and the temperature varied but very little, the maxima 

 ranging from 61° to 66*^ F. by day and the minima from 57° to 61° by 

 night, so that the effects from this cause may be practically put on 

 one side. Similarly the humidity of the air of the room may be neg- 

 lected. They were all carried on between the months of May and 

 September. 



* Bot. Zdt., 1860, p. 113. 



t Elements dc Botanique, 2'"<= ed. 1877, p. 289. 



X Even in this case we meet with a difficulty, in that after several days the 

 absence of air to the roots is liable to cause small and delicate plants to suffer ; 

 so that other precautions must be taken with them, in not allowing the soil to 

 be too wet, and in admitting air from time to time. 



