129 
;7Lateral axis and dorsi-ventral axis about equal. 
2. Picea rubra (Lamb.) Link. Strengthening cells very thick walled, 
occurring in a single row, sometimes doubled or tripled at the angles. 
Some strengthening cells occur within the sheath. 
**Ducts none to tio. 
3. Picea pungens Engelmann. Strengthening cells thick walled, some 
thick-walled cells occurring singly or in groups between the stomata, with 
tendency to double row at the angles. 
4. Picea Engelmanni Engelmann. Strengthening cells in a Single row, 
sometimes doubled at the angles; thick walled. A single cell sometimes 
occurs within the bundle sheath. 
*** Ducts none to one. 
5. Picea Canadensis (Will.) B.S. P. (=Picea alba Link.). Strengthening 
cells in a single row sometimes doubled at the angles; very thick walled; 
some occur within bundle sheath. 
Although the above synoptical arrangements appear to be conclusive 
within themselves they are valuable only in conjunction with the external 
features. 
A PrRotTeotytic ENZYME OF YEAST. 
By KatHERINE E. GoLpeEn. 
INTRODUCTION. 
The enzymes are auxiliary substances which are formed where solid 
bodies are to be liquefied. They are peculiar in that they decompose com- 
plex substances without being affected themselves in any way by the ac- 
tion, and also that even in minute quantities they can produce very 
marked results. They are important in animal and plant metabolism and 
occur both in the cells and in solution in secretions of the cells. In the 
case of unicellular organisms, the metabolic processes are carried on 
throughout their entire substance, the food substance being absorbed into 
the cell, where the enzyme is formed and does its work. This, however, 
is not always the case, the enzyme sometimes being excreted, the work of 
absorption following its action. This latter process is peculiar to multi- 
cellular organisms, having certain parts differentiated for special work, 
9—Science. 
