MR. GLAISUEK ON TEMPERATURE OF ROOTS OF PLANTS. 25 
Y. On a Thermometer for Taking Temperature at the Roots of 
Plants. By James Glaishek, F.E.S. 
[Read June 26, 1872.] 
The temperature of the soil at different depths must more or 
less occupy the attention of gardeners and agriculturists, and more 
particularly in relation to the temperature to which the roots of 
plants are exposed. We possess but little information, even in 
experimental horticulture, as to the temperature of roots, uor of 
the luxuriance of some plants compared to others, which probably 
may be partly attributed to the different temperatures of their 
respective roots. 
We know that improved culture improves plants; we know 
that temperature exercises a great influence, and it is probable that 
the temperature which reaches the roots is that which exercises 
the greatest influence. Considering, therefore, that the ascertain- 
ment of the temperature to which roots are subjected, in connec- 
tion with their more or less luxuriance of foliage, of fruits, or of 
flowers, opens up an unexplored field of information necessary to 
the complete success of the labours of the gardener and^ horticul- 
turist, I have for some time considered how best this information 
could be obtained, and have designed a thermometer with a toler- 
ably sensitive bulb, which may be placed either at 1 inch, 2 
inches, or 3 inches below the surface of the soil — a depth known 
definitely by a circular plate fixed upon the stem of the thermo- 
meter by bayonet joints, resting on the surface of the soil at 1 inch, 
2 inches, or 3 inches from the centre of the bulb of the thermo- 
meter. I have considered it desirable that the whole instru- 
ment should be encased, both for its safety in carriage from 
place to place, and when in use that neither stones nor cats should 
injure it. 
One of these is exhibited (fig. a), prepared for observation at 
these depths. The price of this instrument is 12s. 6d., to be fur- 
nished by Mr. Ackland, of Horne and Thornewaite's, 123, IS'ewgate 
Street, under the condition that it has been previously examined 
and certified by myself as to its accuracy, and that no error so 
much as three-tenths of a degree shall be present at any part of 
the scale. 
An instrument of this form for a depth of 6 inches would be 
17s. 6d., under the same conditions of my examination before sale. 
As most roots are within 6 inches of the surface, these instruments 
