437 



soon as this pressure has ruptured the epidermis (e) at the highest point of 

 the excrescence (se) the ends of the paHsade parenchyma, which are now 

 freed, swell up like clubs (kp) and, turning brown, thicken their walls more 

 or less farther back. The epidermal cells which are ruptured, and others 

 in the same region, turn brown and partially collapse. 



The same swelling can also occur on the side of the leaf. In this case, 

 the spongy parenchyma cells lying directly beneath the epidermis, covered 

 with hairs (h) and otherwise usually isodiametric, become long and 

 cylindrical. 



In various epidermal cells of the upper as well as the lower side of the 

 leaf and in many of the parenchyma cells which have grown out like tubes, 

 glycerin draws together in indi- 

 vidual large glucose drops or many 

 small ones. 



I found similar leaf distensions 

 in Acacia longifolia and A. micro- 

 botrya leaves specked with yellow 

 and also on those normally green. 

 Myrmecodia cchinata is an ex- 

 ample of the general appearance of 

 intumescences with cork leaves. 

 The leaves of this plant usually de- 

 velop intumescences on the lower 

 side, while the cork excrescences 

 predominate on the upper side. In 

 Fig 76 we perceive that actually 

 both of the parencyma layers lying 

 next to the epidermis participate in 

 the formation of the delicate gland- 

 like outgrowth of the tissue. The 

 epidermis (c) (its stomata are un- 

 changed) is raised up and ruptured 

 where it joins the normal tissue. 

 Strange to say, however, it appears 



to be still unbrowned and turgescent, i. e., still completely and sufficiently 

 nourished Hke the tube-like mesophyll cells (a). I found that the excres- 

 cences had dried up and had been cut oil" from the healthy parenchyma by 

 the formation of the layer of flattened cork cells at their base {h) only 

 when the leaf was well advanced in age. 



The partially blister-like, partially wart-like cork excrescences are most 

 frequently found without intumescences. They are distributed irregularly 

 over the whole leaf surface as rusty, sometimes silvery shining specks ; the 

 region of the mid-rib is most afifected. 



The cork forms first within the epidermal cells, advancing thence into 

 the mesophyll, attacking at first two adjoining layers of the hypoderm. 



Fig-. 76. Piece of a leaf of Myrmecodia 

 echinata with a cork wart breaking- out 

 on the upper side and gland-like intu- 

 mescence on the under side. (Orig.) 



