I896-97-] THE GAMETOPHYTE OF BOTRYCHIUM VIRGINIANUM. 283 



quite fully matured ; a^ is the foliar trace of the cotyledon, which is just 

 being separated by a layer of decidual periderm ; x is the central 

 cylinder of a, with the trace of the second leaf just making its appear- 

 ance ; d^ is the still embryonic second root of the smaller embryo <^ ; 

 <^3 is the young cotyledon and j is the central cylinder. Figure 58 

 represents a lower section in the same series with the same lettering as 

 before ; a^ is the primary root of the better developed embryo, and d^ is 

 that of the smaller embryo. At a^ is a prominence indicating the point 

 of origin of the second root of the larger embryo. Figure 59 is of a 

 section still lower down and passes through the common foot of the 

 geminal sporophytes. The staining alone indicates the boundary 

 between the two plants. Their central cylinders are separate throughout, 

 but the fundamental tissues appear to be in textural continuity. A quite 

 sharp demarcation, however, is produced by the different condition of 

 nutrition of their cells ; those on the side of a being loaded with starch ; 

 those of d, on the other hand, containing only a very small amount. 

 Unwillingness to sacrifice the series prevented the use of the ordinary 

 methods of demonstrating protoplasmic continuity for the purpose of 

 discovering whether the protoplasm of the two was in reality continuous. 

 The phenomena of nutrition would seem to negative such a supposition. 

 Figures 57, 58 and 59 have been lithographed from photomicrographs. 



The first root of the young sporophyte is sometimes diarchous, but 

 just as often triarchous. There seems to be no relation between the 

 vigor of the root and the number of protoxlyem-strands ; as depauperate 

 plants sometimes have three strands, and, on the other hand, robust 

 individuals often have only two. I have not found a single example of 

 a monarchous root in the large number of specimens which I have 

 examined. Figure 60 is a drawing of a section of a diarchous primary 

 root in aqueous analinsulphate. The endodermis a is quite distinct, and 

 shows plainly the characteristic radial lignified zones. Between it and 

 the vascular tissue are one or more layers of pericycle cells. The 

 protoxylem tracheides, x, are reticulate in their sculpture and not ringed 

 or spiral as is generally the case. The metaxylem elements almost 

 always meet in the centre. The bast, j, is made up of thick-walled 

 elements, some of which are sieve-tubes and the rest elongated 

 parenchyma cells. Between the bast and the vessels, is a considerable 

 amount of wood parenchyma. Often two or three diarchous roots are 

 formed, but sooner or later triarchous, and finally tetrarchous ones are 

 produced. 



The central cylinder of the stem becomes fully differentiated below 

 the point of origin of the cotyledon. From the very first it has a well- 



