242 PLANT PHYSIOLOGY AND ECOLOGY 



not very mobile, except when they are minute, or are provided 

 with wings or hairs. 



3. Fruit-distributed. The modifications of the fruit for dis- 

 tribution exceed in number and variety all other modifications 

 for this purpose. Many structures, such as the achene, caryopsis, 

 perigynium, utricle, etc., which are commonly mistaken for seeds, 

 belong here. 



4. Offshoot-distributed, To this group are referred all plants 

 that produce lateral shoots, such as root-sprouts, rhizomes, runners, 

 stolons, etc. The migration of such plants is very slow, but it is 

 unusually effective, since the new plant is nourished by the parent 

 until it becomes fully established. 



5. Plant-distributed. This group includes submerged and 

 surface water plants, both motile and non-motile, and those land 

 forms in which the whole plant, or at least the aerial part, is dis- 

 tributed, as in tumble-weeds and many grasses. 



257. Modifications for migration. Plants are arranged in the 

 following groups according to the nature of the device by which 

 migration is brought about. 



L Saccate (saccospores). The species of this group possess 

 various fruits all of which agree in having a sack-like envelope. 

 This may be membranous and serve for wind-distribution, as in 

 Ostrya, Physalis, and Staphylea, or impervious and air-containing, 

 as in Carex, Nymiphcsa, etc., where it serves for water-transport. 



2. Winged (pterospores). This group includes all winged, 

 margined, or flattened fruits and seeds, such as are found in Acer, 

 Betula, Rumex, many Umhellijerce, Graminacece, etc. 



3. Comate (comospores). To this group belong those fruits 

 and seeds with long silky hairs. Anemone, Asclepias, Gossypium, 

 etc., and those with straight capillary hairs or bristles not confined 

 to one end, Salix, Typha, etc. 



4. Parachute (petasospores). These are the parachute-like 

 achenes of Laduca, Taraxacum, and other ligulate composites. 

 Through Eriophorum, Senecio, etc., this group is connected with 

 the preceding one. Parachute fruits represent the highest degree 

 of mobility that has beenobtained by special modification. 



5. Chaffy (carphospores). In this group are placed those 

 achenes with a more or less scaly or chaffy pappus which gives 

 slight mobility, as in Brauneria, Helianthus, etc. 



6. Plumed (lophospores). In fruits of this kind the style is 



