16 BULLETIN 183, U. S. DEPARTMENT OF AGRICULTURE. 



are gorged not only with their own products of conversion but with 

 those of the cells lying beyond them. 



As must be evident from the writers' opposition to the theories of 

 self-digestion and of aleurone activity, their investigations have been 

 overwhelmingly in favor of placing the entire function of diastase 

 secretion during germination upon the scutellum. Morphological 

 examinations have been made of thousands of barley grains at all 

 stages of germination. These have been repeated with a large num- 

 ber of varieties and types of barleys grown under varying conditions 

 in America and of seed imported from all parts of the world. In all 

 cases, the dissolution of the endosperm is effected in the same manner. 

 The corrosion conunences with the parts directly in contact with the 

 scutellum. The action begins as quickly in front of the cells in the 

 center of the scutellum as it does in those next to its peripheiy and 

 therefore in juxtaposition to the a.leurone layer. All later action is 

 such as would occur if the scutellum were the only source of diastase. 

 A grain from which the aleurone layer is removed is converted in the 

 usual manner. Moreover, the very appearance of the scutellum is 

 cojivincing. On its surface is the epithelial layer, which is typically 

 glandular. There are in plant growth no tissues that closely resemble 

 specialized secreting tissues, and seldom is there a more unmistakable 

 development of this than the epithelial layer, as shown in Plate V, 

 figure 1. 



Most investigators have recognized the secreting power of the 

 scutellum; indeed, none have denied such function, even when 

 attributing to it only a subsidiary activity. Numerous experiments 

 have been made in the past and many of them repeated by the 

 wi-iters. A grain from which the embryo is removed will not show 

 any tendency to germination, even though all external conditions, 

 such as light, heat, and moisture be made favorable and ample pro- 

 vision for the removal of conversion products be made. On the other 

 hand, and under proper artificial conditions, the scutellum is able to 

 support itself and to supply food for the growth of the plumule and 

 radicle independent of the endosperm. Morris and Brown, Hansteen, 

 Pfefi^er, and numerous others have shown the ability of the embryo 

 (with the scutellum) to digest the starch supplied to it. This has been 

 demonstrated in numerous ways. The starch has been furnished in 

 the form of macerated endosperm and in the form of a mixture of 

 starch and plaster. In every case, the scutellum was able to corrode 

 the material supplied and to promote a considerable growth in the 

 plantlet. The embryo is also able to utilize an endosperm which is 

 entirely without living protoplasm. An excised embryo from a 

 healthy, vital grain can be grafted upon a dead endosperm with per 

 feet success. Such endosperm may be prepared in any way desired, 

 even by prolonged soaking in absolute alcohol; that is to say, after 



