44 HORTICULTURE FOR SCHOOLS 



55. How plants come up. Each of these two groups of 

 plants has its own method of coming up through the soil. 

 The young monocotyledons have the leaves in a compact 

 roll ending in a sharp point, which is forced up through the 

 soil as the plant grows. After the leaves are through, they 

 gradually unroll and spread out. On account of the manner 

 in which the leaves come through the soil, monocotyledonous 

 plants can get a start in very heavy compact soils, as is seen 

 in the grasses. 



Because of the large size of the leaves and the manner in 

 which they are folded in the bud, dicotyledons cannot, as a 

 rule, successfully push their tops through 

 the soil, especially in cases in which 

 the cotyledons are brought out of the 

 ground ; therefore, the tops of such plants 

 are pulled up by means of the stem 

 (Fig. 25). 



56. Seed dissemination. -Nature has 

 provided for the distribution of seeds 

 by various methods. Some seeds, as 

 those of the thistle, milkweed, cottonwood, and dandelion, 

 are provided with a downy covering or pappus which enables 

 them to be carried long distances by the wind. Seeds of the 

 maple, ash, elm, box-elder, linden, and many of the cone- 

 bearing trees possess wing-like structures which enable them 

 to sail through the air as they fall. Seeds which float easily, 

 as acorns, nuts, and seeds of water plants, are transported 

 readily by running water. Water from irrigation ditches 

 frequently spreads weed seeds in this way. Many seeds have 

 sticky coverings, or hooked appendages, which enable them 

 to hold on to the wool and hair of animals. Beggar-ticks, 

 stick-tights, and burdock seeds are examples. Some seeds 

 are thrown explosively a number of feet, as in the mistletoe. 

 Many pod-bearing plants, of which the touch-me-not is an 

 example, throw their seeds by the contraction and curling up 



