240 



Practical Plant Biology. 



as the first leaf or cotyledon. At the base of it on one side of the 

 embryo is a group of small cells which differentiates as the apex of 

 the stem. In this embryo the apex of the stem is lateral and the 

 single cotyledon terminal. Angiosperms which develop in this way 

 are called Monocotyledons while those which have an embryo with 

 two seed-leaves and a terminal apex are called Dicotyledons. 

 The difference is most marked at germination and is then readily 

 recognisable without microscopic dissection. Later on, the two 

 seed-leaves of the Dicotyledons are with- 

 drawn from the seed and appear above 

 ground usually as two entire green leaves, 

 or remain within the seed and are easily 

 recognised when the seed-coat is removed. 

 But the single seed-leaf of a Monocotyle- 

 don remains attached as a rule in the seed 

 and the first green leaf to appear above 

 ground is also single. It is formed on 

 the opposite side of the young stem to 

 the first seed-leaf and alternates with it. 



It is found that several important char- 

 acters combine to distinguish the Mono- 

 cotyledons from the Dicotyledons and we 

 will now concentrate our attention on our 

 example of the former and note some of 

 the particulars in which it differs from the 

 Buttercup which we chose as a representa- 

 tive of the Dicotyledons. 



The wild Hyacinth (Scilla nutans] 

 grows naturally in open woods. It has 

 long strap-shaped foliage-leaves 20-40 cm. 

 long and 1-5-2-0 cm. wide. From among 

 these rise slender flowering stems each 

 supporting near its top eight or ten bell- 

 shaped blue flowers. The flower-stem 

 bends gracefully under their weight. Each of these flowers is 

 attached to the stem by a short flexible stalk which springs from 

 between two small blue-purple scales (bracts). 



If a plant is dug up it will be found that below the surface of 

 the soil the leaves become white and are expanded round a bulb- 

 shaped mass. At the base of this bulb are found membranous 

 scales which are the remains of the bases of the preceding year's 

 foliage-leaves. From the base of the bulb issue a number of cord- 

 like whitish-brown roots. 



FIG. 86. Scilla nutans. 



