SECT. I 



MORPHOLOGY 



67 



starch, it follows that flour is the richer or poorer in albumen, the more or less 

 completely this outer layer has been removed before the wheat is ground. The 

 aleurone layer remains attached to the inner layer of the seed-coat, in the bran. 

 Reactions for aleurone are the same 



B 



3 



Fig. 69. — A, Cell from the endosperm of Jiicinus 

 communis, in water ; B, isolated aleurone grains 

 in olive oil ; k, albumen crystals ; <j, globoid. 

 (X 540.) 



belonging to the 



as those already mentioned for the 



albuminous substance of protoplasm. 



Treatment of a cross-section of a grain 



of wheat (Fig. 70) with a solution of 



iodine would give the aleurone layer 



a yellow-brown colour, while the 



starch layers would be coloured blue. 

 Albumen Crystals. — Crystals of 



albumen are of relatively frequent 



occurrence in vegetable tissues and are 



often found in aleurone grains (Fig. 



69). Their appearance in the seed 



of Mcimis has been described above, 



and especially large crystals are found 



in the endosperm of the Brazil nut {Bertholletia excelsa 



Lecythidaceae. They have previously been mentioned as occurring in the 



chromatoijhores. In the illustration of the leucoplasts of Phajus grandifolms 



(Fig. 68), the rod-shaped crystals are represented as light stripes (in B and E). 



Albumen crystals may also occur directly in the cytoplasm ; as, for instance, in 



the cells poor in starch, in the 

 peripheral layers of potatoes. Al- 

 bumen crystals are sometimes found 

 even in the cell nucleus. This is 

 particularly the case in the Tooth- 

 wort {Lathraca squamaria), and in 

 many Scrophulariaceae and Ole- 

 aceae (^5). Albumen crystals usu- 

 ally belong either to the regular or 

 to the hexagonal crystal system. 

 They differ from other crystals in 

 that, like dead albuminous sub- 

 stances, they may be stained, and 

 also in that they are capable of 

 swelling by imbibition. Subjected 

 to the action of water or a dilute 

 solution of caustic potash, they at 

 first increase in size without losing 

 their crystalline form. 



Fig. 70. — Part of a section of a grain of wheat, 2'riticum 

 vuhjare. p, Pericarp ; t, seed coat, internal to which 

 is the endosperm ; al, aleurone grains ; am, starch 

 grains; /;, cell nncleus. (x 240.) 



Crystals of Calcium 

 Oxalate. — Few plants are 

 devoid of such crystals. They are formed in the cytoplasm, within vacu- 

 oles which afterwards enlarge and sometimes almost fill the whole cell. 

 In such cases the other components of the cell become greatly reduced ; 

 the cell walls at the same time often become corky, and the whole 

 cell becomes merely a repository for the crystal. The crystals may 

 be developed singly in a c^ll, in which case they are of consider- 



