THE LOCALISATION OF ENZYMES IN PLANTS. 351 



ferment-secreting cells occur in the midst of those containing 

 reserve materials, but not possessing any themselves. This 

 has been noted with wonderful care, patience and precision, 

 by Guignard (7), (9) and (17), in his researches on the 

 Cruciferse and other natural orders, which have already been 

 alluded to. The first case in which successful investigations 

 were made was the root of the horse-radish. Using the 

 micro-chemical tests that we described above, special cells 

 were detected among the parenchyma of different regions, 

 which indicated the enzyme they contained by the character 

 of their protoplasm and their contents. They formed no 

 regular bands of tissue, nor were they usually grouped to- 

 gether ; in transverse diameter they were about the same 

 as those in which they were embedded, though they were a 

 little larger as seen in longitudinal sections. In various 

 parts of the root they varied in size, shape, and degree of 

 aggregation. 



A very prolonged and painstaking series of researches 

 has given us valuable results in localising these secreting 

 cells. Begun originally on the root of the horse-radish, 

 they have been extended throughout the natural orders, 

 Cruciferse, Capparidaceae, Resedaceae, Tropaeolaceae, and 

 Limnanthaceae, and the various regions of typical mem- 

 bers of all these groups have been carefully scrutinised. 

 One fact comes out in them all, and in all parts of them, 

 that the ferment and the glucoside on which the ferment 

 works are always enclosed in different cells. The distribu- 

 tion may be briefly summarised as follows : — 



Roots. — Chiefly in the cortex, but sparsely in the wood. 

 In fleshy roots the tissue representing the wood is 

 mainly parenchymatous, and contains them. In 

 woody roots they are found in the secondary bast 

 as well as in the cortex, and to a less extent in the 

 medullary rays. In the Capparidaceae the wood con- 

 tains none, but some are found in the pith. In the 

 Resedaceae they do not occur farther inwards than 

 the bast. 

 Steins. — There is a good deal of variety observable in 

 different species. Speaking broadly, the pericycle 



