138 OEEMINATION, GROWTH, TISSUE TENSION. 



In germination the radicle grows out, splitting the peri- 

 carp, and the hypocotyl grows vigorously, carrying up the 

 cotyledons often with the split pericarp over their edges 

 like a clip. The hypocotyl is at first bent downward, or 

 coiled in a loop, at the top. This appearance is seen in 

 many seedlings, whether the cotyledons are hypogeal or 

 epigeal in the former case the epicotyl (plumule-axis) is 

 hooked, in the latter case the hypocotyl. The cotyledons 

 turn green, diverge (throwing off the empty pericarp if it 

 has not fallen already), and spread out to the light, also 

 growing larger. At first the plumule grows very slowly, 

 as is usual in seedlings with epigeal cotyledons which 

 function as foliage-leaves ; note the hairiness of the epicotyl 

 as compared with the smooth hypocotyl. 



176. Other Non endospermic Seeds. Examine seeds and 

 seedlings of Linseed, Radish, Cress, Mustard, Turnip, "Nastur- 

 tium" (Tropaeolum), Lupin, Marrow or Cucumber, Horse Chestnut; 

 also the achenes and seedlings of Oak and Sycamore, and the seed- 

 lings of Beech and Gorse. Test cut surfaces of the seeds for starch, 

 proteids, oil ; examine thin sections with the microscope ; dissect 

 the seeds ; sketch stages in germination. 



Sow the seeds in moist sawdust or soil ; note the temperature 

 required (or most favourable) for germination in each case ; examine 

 and sketch the seedlings from time to time. In moistened seeds of 

 Linseed, Cress, Mustard, and Turnip, notice the jelly formed by the 

 swelling of the gnmmy seed-coat when it absorbs water. 



Small seeds e.g. Cress, Mustard, Wheat should be grown on 

 muslin stretched across a tumbler filled with water examine the 

 roots for rootlets and root-hairs. 



In nearly all cases the cotyledons are carried up into the air by 

 the lengthening of the hypocotyl. In Horse Chestnut the large 

 cotyledons are partly fused together ; on germination the young 

 stem and root are pushed out of the seed by the lengthening of the 

 cotyledon stalks. In Vegetable Marrow and Cucumber note that an 

 outgrowth ("peg" or "heel") is formed to hold down the lower half 

 of the seed-coat against the soil, while the growing hypocotyl raises 

 the upper half of the seed-coat and thus gets free. 



In Mustard the cotyledons are two-lobed, in Cress they are three- 

 lobed. In the " Nasturtium " (Tropaeolum majus) the later leaves 

 have a nearly circular blade with even margin, and the stalk is 

 inserted at the centre of the lower side of the blade, but in the ear- 

 liest leaves of the seedling the leaf-blade is lobed and the stalk in- 

 serted at the lower margin, as in the adult leaves of the closely- 

 allied leaves of the Canary Creeper (T. canariense). In Gorse the 



