35° SCIENCE PROGRESS. 



quantity, not only in various parts of a plant, but in the 

 same part at different times. In the resting potato tuber, for 

 instance, little can be detected ; but as germination begins, 

 the enzyme makes its appearance close to the growing part, 

 and later, appears regularly farther in the interior (14), till 

 it can be found throughout its substance. Diurnal variation 

 has been noted in the case of leaves, more being found in 

 the early morning than at sunset, the quantity gradually 

 increasing as darkness advances (2). 



Diastase is, however, the only enzyme which has such a 

 wide distribution. Most other reserve matters than starch 

 are deposited in very definite parts of the plant, and their 

 appropriate enzymes are generally restricted to similar 

 confined areas. The enzyme that most resembles dias- 

 tase in being found in a variety of tissue is vegetable 

 rennet, though the latter does not occur, as does the former, 

 in nearly all plants. We find rennet in seeds, both during 

 and before germination ; in fruits and flowers, even in the 

 bast of certain stems. It is difficult to explain its wide- 

 spread presence, because we do not yet know exactly what 

 decomposition it sets up. Other enzymes, whose working 

 is more fully known, are much more limited in their distri- 

 bution. We begin to find a glandular tissue hinted at, 

 though the same cells often function as storehouses. Thus 

 the proteolytic ferment may be found in the cells of the 

 seeds of various members of the natural order Leguminosa;, 

 particularly in those of the cotyledons (15), where it extends 

 very uniformly throughout the cells. There is not in 

 such a structure a differentiation which can be detected 

 in more complex cases where a gradual process of diges- 

 tion can be seen to spread from certain definite starting- 

 points. An irregular or patchy digestion can be seen in 

 the disappearance of the oil from the endosperm cells of 

 Ricinus communis (16). 



This rudimentary differentiation does, however, lead up 

 to a higher one, where certain cells secrete enzyme only, 

 and in tracing this increase of complexity, we can note it 

 taking place very gradually. We can notice, first, as a 

 stage just beyond the one last described, cases where special 



