198 PROCEEDINGS OF THE 



paired seed-leaves of the dicotyledon is obvious where they push 

 above the ground and spread horizontally to form the first pair 

 of green leaves, between which is protected the bud of the main 

 stem ; and in the pea, acorn, etc., where the seed-leaves are en- 

 larged to act as a store of nourishment and are never raised above 

 the soil, the resemblance to a pair of leaves protecting the main 

 bud is still obvious. The function of the cotyledons is nutritive 

 and protective. During germination they absorb the food 

 material by which the embryo is generally more or less surrounded 

 for the benefit of the seedling and protect the plumule or stem- 

 bud while it emerges from the seed-coat. In monocotyledons 

 the leaf- character of the cotyledon is less generally obvious. In 

 the simplest case the tip remains in the seed till the endosperm is 

 absorbed, then it becomes free, straightens out, and forms the 

 first green leaf, and the first true leaves break through its sheathing 

 base in succession. More often the tip of the cotyledon forms a 

 sucker, which remains in the seed and is connected with the sheath 

 (through which the first leaf of the stem-bud grows) by a longer 

 or shorter portion. From this we pass to the highly specialised 

 grass-type. Here the sucker (scutellum) is a very definite organ, 

 while the germ-sheath protecting the stem-bud (pileole) forms 

 the first green blade. In many grasses there is a small scale-like 

 appendage opposite the scutellum, the epiblast. The scutellum, 

 epiblast and germ- sheath have been variously interpreted, in 

 seeking an explanation of the grass cotyledon, as representing a 

 single leaf or two or three leaves. Comparison with the other 

 monocotyledonous seedlings suggests that the scutellum is the 

 sucker and the germ-sheath the sheath of one and the same 

 cotyledon. On this view the epiblast and the apparent internode 

 (mesocotyl), which sometimes occurs between the scutellum and 

 germ-sheath, require explanation. There are various other inter- 

 pretations. Mirbel regarded the scutellum as the cotyledon, the 

 epiblast as a rudimentary second cotyledon, and the germ-sheath 

 as the first green leaf. Richard explained the scutellum and 

 epiblast as being a distinct absorptive organ, and the sheath as 

 the cotyledon, and Schleiden called the scutellum the cotyledon, 

 the epiblast part of its sheath, and the sheath the first leaf. Dr. 

 Rendle then proceeded to show that if the development and 

 anatomy of the grass embryo be studied, the view derived from 

 our comparative study is supported. 



