82 
ADA HAYDEN 
Bifacial. 
(1) One layer palisade; spongy parenchyma loose. 
(2) One layer palisade; spongy parenchyma loose. 
(3) Two layers palisade; spongy parenchyma loose. 
(4) Two layers palisade; spongy parenchyma loose. 
(5) One- two layers palisade; spongy parenchyma loose. 
(6) Three layers palisade; spongy parenchyma loose. 
(7) One-three layers palisade ; spongy parenchyma loose. 
Homogeneous. 
(1) Rather compact mesophyll (Grass). 
(2) Rather compact mesophyll (Grass). 
Mimulus ringens studied in two habitats shows in one location two layers 
of palisade and a relatively thick outer epidermis, while in the moister 
habitat it has a uniformly thin epidermis and one layer of palisade with a 
thicker area of spongy parenchyma. 
Polygonum Muhlenhergii shows a development of trichomes and a thicker 
paHsade in leaves growing a few rods from a pond, while in shallow water 
its leaves are smooth and have a narrower palisade. 
The Compositae and Gramineae by far exceed the other famiUes in 
both number of representative species and individuals thereof. 
Compositae. The Compositae show considerable variation of tissues, 
but are characterized by prominent palisade, four of the leaves having a 
centric structure, two subcentric, and four bifacial with deep palisade. 
The spongy tissue where present is loose. On low, wet land trichomes are 
generally not developed. Thickened epidermal walls are representative. 
The leaves are characterized by intensive photosynthetic activities. A 
tissue may be represented by an anatomical equivalent under different 
conditions indicating adaptability to habitat, manifested not only in ana- 
tomical characters but through evidence of wide distribution and great 
numbers. 
All these Solidagos have well developed palisade but each of a different 
type. 6". rigida has the driest habitat and shows the most prominent pali- 
sade, cuticle, and trichome development. The leaves appressed to the 
stem are associated with the presence of stomata on both sides. S. serotina 
has a moist habitat and shows practically no protective devices, having 
epidermal walls with loose spongy parenchyma. S. graminifoUa, though 
growing in as moist, if not a moister, habitat than S. serotina, has a thicker 
cut'cle and more compact parenchyma with two layers of palisade. S. 
canadensis has a fairly dry habitat though not so dry as that of 5. rigida. 
Its compact tissue, prominent palisade, and thick- walled hairy ep^'dermis 
seem consistent with its location. 
Gramineae. The grasses of the lowland show a thinner epidermis, 
fewer and smaller bulliform cells, and less spec^'alized palisade in the alluvial 
