36 Principles of Plant Culture. 



46. The Cotyledons (co-ty-le'-dons). In the bean and 

 pumpkin, the seed, or what remains of it, seems to have 

 separated into two parts that are united at one end the 

 cotyledons or seed-leaves. In the bean and pumpkin, the 

 cotyledons form a pair of clumsy leaves, which in the 

 bean, point downward at first, but afterwards become up- 

 right, by the straightening of the hypocotyl beneath 

 them. We observe that the pea has also a pair of coty- 

 ledons (c), which have not separated to the same extent 

 as those of the bean and pumpkin and are still beneath the 

 soil. The corn, in common with other plants of its class, 

 as sorghum, sugar cane, the reeds, grasses, etc., has but 

 one cotyledon, and that is not easily seen without dis- 

 secting the seed. In Fig. 14, which shows a cross- 

 section of the germinating corn grain, the cotyledon ap- 

 pears at cot. 



The plants having two cotyledons form a very import- 

 ant class in botany, known as Dicotyledones (di-co-tyl-e'- 

 dones); those having but one cotyledon form a class 

 known as Monocotyledones (ino'-iio-co-tyl-e'-dones). 

 There is also a class, including the pine, fir and other 

 conifers, that have several cotyledons. 



47. The Hypocotyl Develops Differently in Different 

 Species. In the pea (Fig. 11) and some other plants, 

 the cotyledons remain in the soil, while in the bean 

 and pumpkin, they have been lifted bodily into the air. 

 This striking difference is due to the fact that in the 

 pea, the hypocotyl lengthens very little in germination, 

 while in the bean and pumpkin, it lengthens compara- 

 tively very much. 



48. Seeds in which the Hypocotyl Lengthens in germi- 

 nation Must Not be Deeply Planted. When seeds of this 



