ALEURONE-LAYER NECTARIES 507 



of the ventral furrow, and it is precisely in this region that solution of 

 starch is longest deferred. The author has further shown that the 

 aleurone-layer is capable of secreting diastase by the following experi- 

 ment. Fragments with a superficial area of several sq. mm. were 

 removed, with the help of fine scissors, from the spermoderm of ger- 

 minating grains of Rye, Wheat and Maize ; the adhering aleurone- 

 layer was then separated from these fragments by careful washing 

 with a weak (1-2 per cent.) solution of sugar, and covered with a 

 paste of Rye-flour or starch. After twenty-four hours most of the 

 starch-grains were already deeply corroded or even broken up. Starch- 

 paste placed upon damp filter paper, to serve as a control, showed little 

 or no corrosion in the same time ; the active corrosion that takes place 

 in contact with the aleurone-layer cannot, therefore, be due to the 

 diastatic activity of Bacteria. 



The diastase secreted by the aleurone-layer is not derived at 

 second-hand from the absorbing epithelium of the scutellum, as Tangl 

 supposed, but is actually produced within the aleurone-cells themselves. 

 This point can also be proved by experiment. For this purpose, a 

 shallow groove must be cut with a scalpel in a dry grain of Maize, 

 parallel to, but just outside, the margin of the scutellum, so as to 

 interrupt the continuity between scutellum and aleurone-layer. When 

 a grain which has been treated in this way germinates, it behaves in 

 precisely the same manner as a normal grain, corrosion and solution of 

 the starch-grains appearing first, as usual, in the cells immediately 

 adjoining the aleurone-layer. 



The diastatic activity of the aleurone-layer generally varies with 

 the rate at which the growing embryo uses up the sugar produced by 

 the hydrolysis of starch. If a grain of Rye or Wheat which has been 

 deprived of its embryo, is induced to germinate, no solution of starch 

 takes place, as Sachs long ago remarked. The aleurone-cells of Maize 

 have some power of secreting diastase in the absence of the embryo, but 

 even here this independent activity comes to end after a few days. 24S 



How far the so-called " aleurone-layers," "albuminous layers " or 

 " protoplasmic layers " which occur in various other families of Phane- 

 rogams, act as digestive glands, is a matter of uncertainty. 



C. NECTARIES. 249 



The sugary secretion [or " nectar "J that serves to attract pol- 

 linating insects to flowers, is produced by special glandular structures, the 

 nectaries (nuptial or floral nectaries), which may be located on any of 

 the various floral organs. The nectar-secreting tissue is generally super- 

 ficial, consisting, in fact, of modified epidermal cells, which are often 

 papillose, or palisade-like in form. Frequently the underlying thin- 



