PTERIDOPHYTA 



295 



shoot. From it are soon cut off two lateral segments, which with the primary 

 leaf-segment give rise to the first whorl of three leaves surrounding the base of 

 the young shoot. From this time on the apical cell of the young shoot grows in 

 the same way as that of the shoots in the mature sporophyte. The root behaves 

 like that of the Fern embryo, and growing vertically downward, penetrates the 

 gametophyte, and enters the earth. The young sporophyte is thus completely 

 surrounded by the gametophyte, like that of the Marattiacese. According to 

 Jeffrey (20), the root in E. hiemale seems to arise from the epibasal half of the 

 embryo, but this is not certain. 



The growth of the primary shoot is limited. After it has formed about a 

 dozen whorls of leaves, which are almost always in threes, its growth stops, and 



B 



FIG. 261. E'quisetum telmateia. Development of embryo. A, venter of recently 

 fertilized archegonium (X 300). B, young embryo. C, D, two cross-sections of a 

 young embryo. E, longitudinal section of an older one. r, root ; st, stem. 



its place is taken by a lateral shoot, which develops from a bud formed at the 

 base of the shoot near the point of junction with the primary root. This second 

 shoot, which grows to be somewhat larger than the primary one, and usually has 

 four-toothed foliar sheaths, is soon replaced by a tertiary shoot formed from a 

 basal bud in the same way. This is repeated until a cluster of slender shoots is 

 formed, when finally a bud is formed at the base of one of them, which grows 

 horizontally into the earth, and forms the rhizome, or underground stem, found 

 in the older sporophyte. 



THE MATURE SPOROPHYTE 



The rhizome, or underground stem, found in all species of Equi- 

 setum, shows the same division into nodes and internodes which is 

 found in the primary shoot. Surrounding the nodes are the leaf- 



