Etherization, as applied to plants, means strictly the forcing of a dormant plant into growth by subjecting the plant to ether vapors at certain concentrations in a closed chamber for a definite period of time, usually twenty-four to seventy-two hours. The plant after such treatment is placed under environmental conditions favorable for growth. Since in practice the use of chloroform is similar in its application and effects, it will be discussed here. The general nature of etherization was first noted by Johannsen in 1890, and following his investigation a wide stimulus was given to the commercial forcing of flowering shrubs. For other methods of forcing a dormant plant, see Rest-period.

Before discussing the method of etherization, its effects and application, it is necessary first to have some idea of what is meant by the term rest-period or the condition of dormancy.

Rest-Period

Perennial plants, especially those in the temperate regions, in general have a season of growth and active metabolism followed by a period of quiescence as regards any outward manifestations of metabolism. During this period, not all of the vital processes are at a standstill and changes in the reserve food may be in progress, but the plant appears to be at rest and is dormant. The rest-period begins with the advent of the unfavorable growth conditions of the autumn, and normally continues until the favorable conditions of the spring.

One might reasonably assume that growing perennial plants removed from out-of-doors at the approach of autumn conditions to a greenhouse, would continue growth and not pass into the rest condition. One might assume, also, that if a plant in a dormant condition be brought into favorable conditions it would resume growth immediately. But experience and investigations show that many plants will not immediately continue growth, and, provided they do continue growth, it is at a slower rate. Dormant plants, that is those in the rest-period, may require considerable time before resuming growth. There are some plants that during dormancy respond quickly when brought into the greenhouse; there are others that remain dormant despite the most favorable environmental conditions. The rest-period in various species of Acer (maple), of Quercus (oak), of Fraxinus (ash), and of Fagus sylvat-ica, as well as other plants, is so well fixed as to make it almost impossible to force the dormant plants into growth by warmth and moisture alone. Special treatment is necessary, such as etherization. There are other plants in which the rest-period is not well established. These quickly respond to favorable growth conditions normally prevailing in a greenhouse.

In many plants this rest-period has attained an almost habitlike character. The following table with data taken from results secured by Howard with branches brought into the greenhouse at Halle, Germany, is instructive:

Growth Response Of Branches When Brought Into Greenhouse

Species

Collected

Oct. 20-Nov. 4,

1905.

No. of days for beginning of growth

Collected Jan. 8-10,

1906. No. of days for beginning of growth

Acer negundo variety versicolor .......

63

20

Acer pseudoplatanus ......

0*

0

Azalea mollis...........

26

0

AEsculus Hippocastanum.

0

20

Betula nigra............

62

12

Berberis vulgaris .....

10

3

Celastrus scandens ...

0

17

Cercis canadensis .......

0

10

Cydonia japonica .....

6

7

Deutzia gracilis .........

10

3

Fagus sulvaticaa .....

0

38

Lonicera tatarica .....

7

3

Magnolia acuminata ...

29

25

Populus canadensis ....

61

20

Quercus marcrocarpa ...

59

0

Spiraea sorbifolia .....

1

.*0=No growth

In the investigation made by Howard, 234 species were collected from October 20 to November 4, and of these only 125 grew; and of the 125, only 18 per cent began growth within a period of nine days. Between January 8 to 10, another collection was made including practically all the species of the first lot and others in addition, so that the number totaled 283 species. Of this number 244 grew, of which 50 per cent began growth within the first nine days. The species that did not grow when brought into the greenhouse January 8 to 10 made growth when brought into the greenhouse on February 26. From these and the results of other experiments the conclusion is drawn that plants in general tend to pass out of the rest condition as the season advances toward the spring. Dormancy is less stable in January than in November. This condition holds true not only for woody plants but also for bulbs and other herbaceous plants.

Method Of Breaking The Rest-Period

The one method which has been largely employed for forcing dormant plants into growth is the etherization method. An air-tight chamber is provided, the size depending on the quantity or size of the material to be treated. The plants being placed in the chamber, it is tightly sealed except for a small opening through which ether may be introduced. Usually just below this opening is placed a sponge on which the ether is poured and then the opening is again sealed. If one desires to etherize a few bulbs, a wide-mouth bottle of two quarts capacity may be employed and the ether added in a small vial and the bottle then tightly stoppered. Special etherizing chambers are described for commercial work. The main desideratum is to have a chamber that will not permit of leakage of the ether vapor. The stopper must be securely fastened or weighted down.

Quantity Of Ether

The quantity of ether best employed in forcing plants may vary with the nature of the plant, the season of the year, and the temperature of the etherization chamber. In general, the quantity to be added varies from 5 to 15 cubic centimeters per cubic foot of space (10 cubic centimeters equal about one-third fluid ounce). Early in the rest-period at 60° F., one should use about 15 cubic centimeters per cubic foot of space. In the middle of the rest-period, one should employ less and the amount should be further decreased toward the end of the rest-period. If the relative humidity of the chamber is high, a slight increase in the quantity of ether may be made. If chloroform is used, the quantity should be one-fourth to one-third of the quantity of ether recommended. The following figures are from Stuart:

Treatment Recommended For Plants At Different Seasons Cubic Centimeters Per Cubic Foot

Ether

Chloroform

Cc.

used

Exposure hours.

Cc.

used

Exposure hours.

Lilac -

October..........

15

48-24-24

4

48-24-24

November....

12

48-24-24

3 1/2

48-24-24

December ....

10

48-24-24

3

48-24-24

January...

..

..

Astilbe -

October.......

15

48-24-48

4

48-24 - 48

November .........

15

48-24-24

48-24-24

December .........

12

48-24-24

48-24-24

January ...........

10

48

3

48

Time Of Exposure

The time of exposure is also variable, being of greater duration in the early part and shorter in the latter part of the rest-period. In the early rest-period, a long exposure is given, varying from forty-eight to seventy-two hours to even as much as ninety-six hours. In case of long exposure, the practice is usually followed of making a forty-eight-hour exposure, after which the plant is removed from the etherization chamber for a day and then re-etherized for another twenty-four-hour period. Toward the middle and late rest-period, the time of exposure may be shortened as well as the quantity of ether.