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 yT, 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 

 Ronpa 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 Ostrya, 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 

 Uinbellifcrae, Graminaccae, etc. 



3. Comate, comospores. To this group belong those fruits arid seeds with 

 long silky hairs, Gossypium, Anemone, Asclcpias, 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 LiguMorae are connected through Senecio 

 and Eriophoriim with the preceding. These represent the highest develop- 

 ment of jnobility 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 

 usually modified into a long plumose organ, possessing a high degree of mo- 

 bility, as in Pulsatilla, Sieversia, and Clematis. 



