32 BULLETIN 844, U. S. DEPARTMENT OF AGRICULTURE. 



Beneath the so-called cuticle there is the much thickened outer 

 portion of the Malpighian cells in which there are two rather distinct 

 regions, one constituting the conelike structures and the other form- 

 ing a continous layer over the conelike structures, separating them 

 from the cuticle and filling in between them. These two regions 

 separate easily, and in cutting sections the outer region, called by 

 some the cuticularized portion, often breaks away, leaving the entire 

 surface of the cones exposed. 



The term " cuticularized layer" will be used to designate aU of the 

 thickening covering the cones, including that around the cones as 

 well as the portion between the cones and the cuticle. This term is 

 not entirely appropriate, for the region is practically free from cutin, 

 but for the want of a better term it will be used. There are canals in 

 the cuticularized layer and cones, which are easily seen when the 

 sections are treated with chloriodid of zinc or sulphuric acid. A 

 surface view of a section showing the cones and cuticularized layer 

 when mounted in glycerin shows the canals as dark lines due to the 

 air inclosed. The canals are most abundant along the lines where 

 the lateral walls of the cells join, but many are within the cones and 

 in the cuticularized substance between the cones. (PI. V, fig. 5.) 



The well-developed light line in Melilotus alba and M. officinalis is 

 found just below the bases of the cones. In some seed coats only a 

 few and in others none of the canals which are common in the cones 

 and cuticularized region cross the light line. A very distinct line of 

 small canals filled with air and thus forming a dark band is present 

 just above the light line, thus making the light line more conspicuous. 

 (PL V, fig. 3.) When the lumina of the cells extend across the light 

 line, they are exceedingly small. The light line is the most compact 

 region of the Malpighian layer and is conspicuous because it refracts 

 the fight much more than the regions above and below it. 



Just below the Malpighian is a layer of cells variously modified 

 and known as the osteosclerid. The cells of this layer are often 

 referred to as the hourglass cells on account of their shape. In some 

 regions of the seed coat they are expanded at both ends and their 

 walls are much thickened, the thickenings forming ridges on the 

 radial walls, while in other regions only the upper tangential wall and 

 a portion of the radial walls are thickened and the cells are expanded 

 only at the inner end, thus having the shape of the frustum of a cone. 

 Beneath the osteosclerid la3^er is the nutrient layer. 



The nutrient layer contains chloroplasts. It varies not only in 

 the number of layers of cells composing it, but also in the modifica- 

 tions of these cells. This layer ranges from four to seven cells in 

 thickness in the different parts of the seed coat. 



