INVASION 213 
sufficiently diverse to indicate that these common species must have entered 
either one by migration from the other, 83 exhibit modifications for dissem- 
ination, while 8 others, though without special contrivances, are readily dis- 
tributed by water, and 4 more are mobile because of minuteness of spore or 
seed. Some degree of mobility is present in 73 per cent of the species com- 
mon to these regions, while of the total number of species in which the mode 
of migration is evident, viz., 95, 66 per cent are wind-distributed, 20 per cent 
animal-distributed, and 14 per cent are water-distributed. It need hardly be 
noted that this accords fully with the prevalence and forcefulness of winds 
in these regions. Of the species peculiar to the foot-hill region, many are 
doubtless indigenous, though a majority have come from the montane regions 
to the westward. The number of mobile species is 121, or 60 per cent of the 
entire number, while the number of wind-distributed ones is 85, or 70 per 
cent of those that are mobile. Among the 25 species found in the widely 
separated wooded bluff and foot-hill regions, 2 only, Amorpha nana and 
Roripa nasturtium, are relatively immobile, but the minute seeds of the lat- 
ter, however, are readily distributed, and the former is altogether infrequent. 
The following groups of plants may be distinguished according to the 
character of the contrivance by which dissemination is secured: 
1. Saccate, saccospores. Here are to be placed a variety of fruits, all of 
which agree, however, in having a membranous envelope or an impervious, 
air-containing pericarp. In Ositrya, Physalis, Staphylea, the modification 
is for wind-distribution, while in Carex, Nymphaea, etc., it is for water- 
transport. 
2. Winged, pterospores. This group includes all winged, margined, and 
flattened fruits and seeds, such as are found in Acer, Betula, Rumex, many 
Umbelliferae, Gramtinaceae, etc. 
3. Comate, comospores. To this group belong those fruits and seeds with 
long silky hairs, Gossypium, Anemone, Asclepias, etc., and those with 
straight capillary hairs or bristles not confined to one end, Typha, Salix, etc. 
4. Parachute, petasospores. The highly developed members of this group, 
Taraxacum, Lactuca, and other Liguliflorae are connected through Senecio 
and Eriophorum with the preceding. These represent the highest develop- 
ment of mobility attained by special modification. © 
5. Chaffy-pappose, carphospores. In this group are placed those achenes 
with a more or less scaly or chaffy pappus with slight mobility, as in Rud- 
beckia, Brauneria, Helianthus, etc. 
6. Plumed, lophospores. In the fruits of this class, the style is the part 
tisually modified into a long plumose organ, possessing a high degree of mo- 
bility, as in Pulsatilia, Sieversia, and Clematis. 
