182 



MINUTE STRUCTURE OF THE SEED. 



510. The embryo may exist as a cluster of parenchyma cells 

 without any clear distinction of parts, or it may possess a defi- 

 nitely formed axis and leaves (see "Structural Botany," p. 311). 



The microscopic structure of the nucleus has been illustrated 

 in part by the figures of the grains of cereals (see also Fig. 22, 

 on page 47), and it has been considered also to some extent in 

 the descriptions of the nascent root and the nascent stem in the 

 embryo. The study of the development of the embryo within 

 the seed belongs to a special subject, which will be treated in 

 Part II. under " Reproduction." It therefore will suffice here to 

 state that the parenchyma cells of which the nucleus is composed 

 contain food materials and protein matters in large amount. 



511. The proper food materials in seeds are chiefly oils and 

 starches. The seeds of a large number of plants have been ex- 

 amined by Niigeli 1 with reference to the occurrence of starch, and 

 the following facts are taken from his extensive treatise : 



512. The protein granules in seeds are classified by Vines 2 as 

 follows : 



1 Die Starkekomer, 1858, p. 387. 



2 Proceedings of the Royal Society, vols. xxviii., xxx., and xxxi. On 

 page 62 of the volume last- mentioned the following table of seeds and their 

 aleurone grains is given : 



I. Soluble in water : Pseonia officinalis (type), Ranunculus acris, Aconitum 



Napellus. Nigella damascena, Helleborus ftetidus, Amygdalus com- 

 munis, Prunus cerasus, Pyrus malus, Leontodon Taraxacum, Dipsa- 

 cus Fullonum, Ipomoea purpurea, Phlox Drummondi, Vitis vinifera. 



II. Completely, and more or less readily, soluble in ten per cent NaCl 



solution. 



