PROCESSES WHICH OCCUR IN VEGETABLE TISSUES. 7 
Supposing the tissue to have been treated with iodine and sul- 
phuric acid, a section will display on the general parenchyma a 
blue-stained phellogen, succeeded by flattened unstained cells of 
cork and a line of red or yellow sclerenchyma, two, three, or even 
four cells deep, these sclerotic cells being ranged in order with 
the flatter cork, and themselves succeeded by flattened suberous 
cells like those which lie beneath them; on the cork are larger 
cubical or spheroidal cells, the deeper unstained, those of the sur- 
face dead and deeply coloured blue. 
Injuries of amputation in Opuntia are healed in a similar 
manner, a partition of sclerenchyma being formed so as to lie in 
the midst ofthe flattened corky layer. The thickening affects first 
the outer wall of the cell; and in later stages the outer walls 
of the cells, or those towards the surface, are often thickened 
in excess of those opposite. Yet this particular mode of repair 
is not so general in the Cactacew that it may be deemed a 
rule. In Mammillaria, for instance, repair is effected by tiers 
of tabular cork and phellogen without the formation of scle- 
renchyma. 
The relationship which the new-formed cells bear to those of 
the general surface may appear, also, in the nature of their 
contents. Thus in the stems of Cacalia articulata, where the 
cells for two or three rows beneath the epidermis are flattened 
and hold cubical or rhomboidal crystals, the flattened cells of 
the repair beneath the cork contain similar crystals, whilst there 
are none such in the cortical parenchyma or in the cells of the 
pith. 
It is interesting to observe, as showing some similarity to 
the reparative process as it occurs in Mammalia, that the cicatri- 
cial tissue does not acquire the full structure of that which it 
replaces. The new tissue is devoid of stomata, which on the 
stems of Cactacez are abundant; nor are such ever formed in, 
nor hairs upon it; as in animal scars, there are produced no 
sweat-glands or hair-follicles. 
It is worthy of note also that the new covering does not spread 
from the edges of the original investment, but that its formation 
occurs simultaneously at all parts of the injured surface. 
Now this process of healing is, in essential respects, parallel 
with the healing beneath a scab as it occurs in animal tissues— 
the form of healing which is most common in animals, and 
the general mode of the healing of open wounds in vegetable 
