EQUISETACEJE 



103 



rapidly disappears entirely ; it undergoes no further division, but elongates 

 rapidly into a long hyaline rhizoid. The larger of the two primary cells, 

 which still contains abundance of chlorophyll, divides further by walls, at 

 first in two directions only, into a multicellular plate which increases 

 rapidly by apical growth, and soon branches in one plane. A difference 

 is now set up between the develop- 

 ment of the male and female pro- 

 thallia. The former remain com- 

 paratively small and narrow, and 

 the cell-division continues in the 



FIG. 78. A. male prothallium of Equisetum 

 arvense L. ; a, antherids ( x 200). (After Hof- 

 meister.) B E, antherozoids of E. maximum 

 Lam. in different stages of development 

 ( x 1200). (After Schacht.) 



two directions only ; they consist, 

 therefore, permanently of only a 

 single layer of cells, and display 

 but little lobing. Their colour is 

 yellowish green. The female pro- 

 thallia, on the other hand, grow to 



a considerably larger size, as much as half an inch in length, are of a 

 deeper green colour, and at an early period form a number of lobes at 

 their anterior portion, which consist of masses of merismatic tissue, cell- 

 division taking place in the tangential as well as the other two directions ; 

 they branch also in the same plane much more abundantly than the male 

 prothallia. The formation of female or male prothallia appears to depend 



FIG. 79. Vertical section of lobe of female pro- 

 thallium of E, arz'ense. a, archegones; h, 

 rhizoids ( x 600). (After Goebel.) 



