GROUP III. PTERIDOPHYTA : EQUISETIN^E. 385 



most layer of the cortex, the endodermis being the last layer but one of the 

 cortex (p. 115). Hence it appears that here, as in the Ferns, the lateral roots 

 spring from the innermost layer of the cortex. There is no pericycle in 

 the root of Equisetum. 



Embryogeny of the Sporophyte. The oospore is divided by a transverse 

 basal wall, and then becomes segmented into octants, as in the Filicinae. 

 Of the four epibasal octants, one gives rise to the growing-point of the 

 primary stem ; two to the first cotyledon ; and the fourth to the second 

 cotyledon : the two cotyledons cohere to form a leaf-sheath round the 

 young primary stem. Of the four hypobasal octants, one gives rise to 

 the growing-point of the primary root, and two to the foot. 



The primary stem grows erect, and its leaf-sheaths are three-toothed, 

 the three leaves corresponding to the three segments cut off from the 

 apical cell of the stem ; it branches at its base ; stouter shoots with an 

 increasing number of teeth in the leaf-sheaths are successively produced, 

 and eventually a branch is produced which becomes the perennial sub- 

 terranean rhizome. 



The GAMETOPHYTK is a green, dorsiventral, lobed prothallium which be- 

 comes quite free from the spore. The prothallia are generally dioecious, 

 the female prothallia being larger than the male ; but the distinction of 

 sex is not absolute, for the female prothallia may eventually bear male 

 organs, and the male prothallia female organs ; it appears to depend 

 largely on conditions of nutrition. 



The germinating spore divides into two cells : one of these contains no 

 chloroplastids, and grows out into a root-hair, the other contains chloro- 

 plastids, and grows and divides to form the first lobe of the prothallium, 

 which branches as its development proceeds, some of the branches of 

 the female prothallia growing erect. On its under surface the prothal- 

 lium bears numerous root-hairs. 



At first the prothallium consists throughout of a single layer of cells ; 

 in the female prothallium, however, one of the lobes becomes thick and 

 fleshy, consisting of several layers of cells formed by repeated horizontal 

 cell-division, and this constitutes the archegoniophore. 



The male organ, or antheridium, is developed from a single cell of the 

 margin of the male prothallium : this cell undergoes repeated division, 

 with the result that a wall, consisting of a single layer of cells, is formed 

 surrounding a central cell from which, by subsequent divisions, the 

 numerous mother-cells of the male cells are developed : the antheridium 

 eventually dehisces by the separation of the cells forming the roof, in 

 consequence of the swelling-up of the contents of the antheridium. The 

 male prothallium bears several antheridia, one being developed terminally 

 on each lobe, and others in succession on the lateral margins. 



The male cell is a spermatozoid, which is larger than that of any other 

 Pteridophyta ; it has only two or three coils, and bears a tuft of short 

 cilia at its anterior pointed end. 



The/ei?e organ, or archegonium, resembles, in all essential features of 

 its structure and development, that of the typical Filicinse : a distinctive 

 peculiarity -is afforded by the long recurved terminal cells of the neck, 

 M.B. C C 



