36 Principles of Plant Culture. 



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 after- 

 wards becomes upright, by the straigtening hypo- 

 cotyl beneath them. We observe that the pea has also 

 a pair of cotyledons (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 dissecting the seed. In Fig. 14, 

 which shows a cross-section of the germinating corn 

 grain, the cotyledon appears at cot. 



The plants having two cotyledons form a very im- 

 portant class in botany, known as Dicotyledones (di-co- 

 tyl-e'-dones) ; those having but one cotyledon form a 

 class known as Monocotyledones (mo'-no-co-tyl-e'- 

 dones). There is also a class, including the pine, fir 

 and other conifers, that have several cotyledons. 



46. 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. 



47. Seeds in which the Hypocotyl Lengthens in ger- 

 mination Must Not be Deeply Planted. When seeds 

 of this class, which includes many plants beside the 



