28 PRINCIPLES OF PLANT GULTUBE 



45. The cotyledons. — 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 upright, by 

 the straightening hypocotyl 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 and the like, 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 important 

 class of plants known in botany as Dicotyledons; those 

 having but one cotyledon form a class known as Mono- 

 cotyledons. There is also a class, including the pine, 

 spruce and other conifers, in which there are several 

 cotyledons. 



46. Development of hypocotyl. — The hypocotyl de- 

 velops 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 

 comparatively very much. 



47. Shallow planting. — Seeds in which the hypocotyl 

 lengthens in germination must not be deeply planted. 

 When seeds of this class, which includes many plants 

 beside the bean and pumpkin, are planted in soil, the 



