The Utilization of Herbarium Material. 105 
Two distinct problems arise: (1) the restoration of the original 
form ; (2) the removal of air which has entered the cells, and is 
often very tenaciously retained. 
The chief material studied was the stem of Helinnthus tuberosus, 
which shows a wide range of histological differentiation, supple¬ 
mented however by floral material from various families, some of 
which was as much as fifty years old. 
Sections of three different thicknesses were laid on filter 
paper in a desiccator, where they stayed for a month, being for six 
days kept at a temperature of 100°C., in order to imitate the effect 
of prolonged air-drying as quickly as possible. After this treatment 
the sections, slightly curled, showed the brown colour of old 
herbarium specimens, and did not regain their form in water alone, 
which is characteristic of material long air-dry. These sections 
were then differentially treated in order to observe the effect of the 
factors involved in recovery, which may be catalogued as:— 
a. Preliminary Treatment. 
b. Size of Material. 
c. Concentration of Medium. 
d. Time. 
e. Temperature. 
To avoid needless detail the most successful treatment will be 
described shortly under each of the above headings. 
a. Preliminary Treatment. Place the material directly into 
Absolute Alcohol, where it should remain for at least 24 hours. 
If the pieces are very delicate or very small, this is all that is 
required, but all pieces of appreciable thickness should be subjected 
to a reduced pressure of below 10 cms. of mercury during their 
immersion, to ensure proper penetration. 
From the Absolute Alcohol bring the material down to distilled 
water through graded alcohols, as customary in cytological work. 
This ensures the complete replacement of the alcohol by water 
throughout the mass, and is very important in providing for the 
regular commencement of the swelling process. 
Once in the water, the pieces may be left there indefinitely. 
The growth of moulds is prevented and recovery greatly hastened 
if they are placed in a hot chamber such as a paraffin oven during 
this period. In this way also much if not all of the brown dis¬ 
colouration may be extracted. All the changes from one medium 
to another must, in point of time, be proportioned to the bulk of 
the material, but roughly speaking the slower they are the better. 
