XIII 



EQUISETINEjE 



431 



subsequently divides by a transverse wall, as may happen in 

 the Marattiaceae and occasionally in Osnimtda, but whether 

 this always takes place is not certain (Fig. 224, A). The four 

 rows of neck cells are all alike, and consist ordinarily of three 

 cells each, the terminal ones being very long, and when the 

 archegonium opens bending back strongly, but not becoming 

 detached. The central cell is surrounded by a single layer of 



Fig. 224. — A, Longitudinal section of nearly ripe archegonium, with two neck canal cells (c, Ci), X550 ; 

 B, section of an open archegonium, x 275 ; C, D, two cross-sections of a young archegonium ; L, 

 the lobe at the base of which the archegonium is formed, X550. 



tabular cells cut off from the adjacent prothallium tissue, but 

 these divisions may extend to the lower neck cells (Fig. 224, 

 A). The egg is globular and shows no peculiarities of structure. 

 Buchtien's ^ account of the further development of the meristem, 

 as well as his figures, point to something very much like a 

 repeated dichotomy of the growing point ; a further investigation 



^ Buchtien ( i ), p. 24. 



