COTYLEDON 



1611 



COUGH 



screens in early summer, or to the continually- 

 falling leaves; but the shade afforded is very 

 welcome. 



A moist, strong, loamy soil is the best for this 

 rapid grower, and cottonwood trees 100 feet 

 high and more are found, along river banks 

 especially, from Florida to Quebec and west 

 to New Mexico and Colorado. They live 

 from fifty to seventy-five years. The wood of 

 this tree is weak, soft and dark brown in color, 

 but is used for packing cases, barrels and 

 boxes, woodenware and for paper pulp. The 

 cottonwood is also known as Carolina poplar 

 and necklace poplar. The name is due to the 

 characteristic cottonlike appearance of the 

 opened seed pods. 



COTYLEDON, hot He' dun, the name com- 

 monly given to the first leaves which sprout 

 from a seed. If a bean be soaked, freed from 

 its skin and then split, it is seen to be com- 

 posed of two thick portions which are attached 



COTYLEDONS 



(a) Bean seedling, showing cotyledons; (6) 

 lengthwise section through embryo end of a 

 grain of wheat; (c) half an acorn cut length- 

 wise, filled with very thick cotyledons. 



to each other only for a very little way. 

 These are the cotyledons, and are not to be 

 confused with the tiny plumule, or leaf folded 

 away near the joining point. When a new bean 

 plant pushes its way through the soil, these 

 thick seed-leaves are clinging to it, but they 

 gradually shrivel and drop off, without even 

 looking like true leaves. All the plants which 

 have their seeds enclosed in cases angio- 

 sperms, to use their scientific name are di- 

 vided into two groups, according to the num- 

 ber of cotyledons. 



Monocotyledons. These are plants which have 

 only one seed-leaf, for mono means one. They 

 include the palms, lilies, sedges and grasses, or 

 grains. A kernel of corn or an onion seed cannot 

 be split easily, as can a bean, for there is no nat- 



ural line of division into two parts. When some 

 of these plants, as the different grains, sprout, 

 the cotyledon remains below the ground and sends 

 up to the growing embryo the liquid food ; while 

 in others, as the onion, the cotyledon appears 

 above the ground but never develops into a true 

 leaf. 



Dicotyledons. This word refers to plants 

 which have two seed-leaves ; they comprise most 

 of the very numerous flowering plants. Some of 

 the seeds are large, like those of the lima bean ; 

 some, as the portulaca, are almost as small as 

 grains of dust, but all have the two seed-leaves. 

 Like the monocotyledons, these plants sometimes 

 thrust the cotyledons above the ground, some- 

 times leave them below, whence they send up as 

 food the reserve material stored in them. 



These two great classes comprise all the 

 flowering plants, but the naked-seed plants, or 

 gymnosperms, form a different class. The seeds 

 of these have more than two seed-leaves, and 

 the group is therefore called polycotyledonous, 

 which means having many cotyledons. See 

 BOTANY; FLOWERS. 



COUCH, kouch, GRASS, a common grass or 

 weed which looks somewhat like wheat. Sheep 

 like it when it first comes above ground, 

 and it makes good hay, but on cultivated land 

 it is a pest. The rootstocks are far-reaching 

 and continue to spread, often piercing roots 

 of other plants. Deep plowing under of in- 

 fested lands in summer, then rolling, grubbing, 

 harrowing and some hand picking will effect- 

 ually remove this weed. Couch grass is also 

 known as quick grass, dog grass, wheat grass, 

 etc., and also as quack grass, because the root- 

 stocks are often used in patent medicines. 

 Its medicinal qualities, however, are nearly if 

 not quite non-existent. The matted roots of a 

 growth of couch grass on a railway embankment 

 are very useful in holding the loose soil to- 

 gether. 



COUGAR, koo'gur. See PUMA. 



COUGH, kawf. If a particle of food or other 

 substance becomes lodged in the throat, or if 

 some foreign substance enters the windpipe or 

 other air passages, we cough to expel it. Cough- 

 ing is produced by an involuntary contraction 

 of the muscles controlling the process of breath- 

 ing. The cause may be irritation, due to the 

 lodging of some substance in the air passages; 

 or to the accumulation of matter in the air pas- 

 sages, resulting from a diseased condition of the 

 lungs or throat, as in case of a cold; or to an 

 irritated condition of the nerves controlling the 

 action of the respiratory muscles. Dizziness in 

 the case of adults and hardened wax in the 

 ear in the case of children, constipation, intes- 

 tinal worms, dyspepsia and liver trouble are 



