Vegetation of the Sotol Country. 
113 
back to the seed condition in the brief season following copious 
rains while the surface soils are supplied with moisture. These 
are well known adaptation devices. 
A systematic presentation of these types will be instructive: 
A. Ecological forms distinguished by marked development of 
storage tissue in one or more of the regions — root, stem, leaf — 
which results in abnormal forms of plants and in special habits 
with respect to the performance of the vital functions. 
I. Storage tissue — for water, reserve foodstuff, mucilage, ex- 
cretion products — chiefly in thick, fleshy, spine protected 
leafless stems; leaves wanting; assimilation tissues in super- 
ficial area of stem. 
Cactus types. 
1. Stems flat jointed; Plat-Opuntias. 
2. Stems spherical or flattened, disk shape. Echinocac- 
tus texensis, horizonthalonius, longihamatus, etc. ; 
cactus heyderi, micromeris, pectinatus, etc.; Ario- 
carpus fissuratus. 
3. Stems cylindrical, fluted. Cereus stramineus, longi- 
spinus and greggii; Opuntia leptocaulis and arbor- 
escens. 
II. Storage tissue — for reserve food, saponin, mucilage, crys- 
tals — in more or less enlarged and succulent, bayonet shaped 
leaves arranged in rosette or close spiral with armed tips 
presenting an abattis-like defense. Roots commonly fleshy, 
much branched and wide spreading. Tendency to develop 
palm-like caudex with food storage in a leaf base region. 
Agave lechuguilla, Yucca radiosa, treculeana, macrocarpa, 
baccata, etc. ; Hesperaloe parviflora. 
Ila. As in II but storage tissue chiefly in roots and short cau- 
dex; leaves narrow, long and grass like; Dasylerion tex- 
anum; Eolina texana, erumpens, and lindheimeriana. 
III. Storage tissue in more or less woody but fleshy stems or 
roots. 
1. Leaves normal, quickly falling. Jatropha spathulata. 
2. Leafless, juncoid stems. Euphorbia antisyphilitica. 
IV. Storage tissue developed in well protected perennial, 
sclerenchymatic roots or in bulbs; aerial parts evanescent, 
coming out soon after rainfall and disappearing with dry 
weather. 1 Jatropha berlandieri and macrorhiza; Alliona, 
iln reality, a large number of species generally thought of as constitut- 
ing the herbaceous annual vegetation fall in this class. 
