Notes. 
623 
a. The purely epidermal and smaller type consists of one or two 
tiers of much elongated, thin-walled cells, usually twisted spirally 
round one another. At the apex is a stoma, which may or may not 
lead into an intercellular space. 
/3. The larger outgrowths contain basal prolongations of paren- 
chyma. 
2 . On the stem the outgrowths are more complex, and usually 
larger. The basal part consists of elongated sub-epidermal cells 
divided by periclinal walls. The upper part is made up of much 
enlarged, thin-walled epidermal cells, similarly divided. The out- 
growths later become cut off by cork, which arises in the lowest 
row of daughter-cells derived from the original epidermis, i. e. in the 
lowest colourless cells ; after suberization of these cells the outgrowth 
shrivels. 
II. Experimental Part . 
Seedlings were raised in the Tropical Pit, and eight of them were 
planted, each in a separate pot, and allowed to grow on under 
identical conditions. They all developed intumescences, and were 
all very much alike. When each had about nine or ten leaves, and 
was beginning to flower, the plants were placed under different condi- 
tions, and examined at the end of six weeks : — 
The plant grown in the open was entirely free from intumescences ; 
it was particularly vigorous, and had strong lateral branches. 
The plant in the temperate house had outgrowths only on the under 
sides of the leaves, and on the flowers and fruits. 
The plant in the filmy fern-house was very unhealthy, but had no * 
outgrowths. 
All the other plants had outgrowths on one or both sides of most 
of the leaves, on the stems, the green parts of the flowers, and on the 
young fruits. 
Conclusions. 
As far as the evidence goes at present, it seems to point to the 
conclusion that the intumescences are pathological, and are due 
neither to insects nor to fungi, but to the direct effects of environment. 
The formation of outgrowths appears to be caused by excessive 
moisture combined with a high temperature. If the temperature is 
low the plants do not appear to have strength to form them. The 
