340 hofmeister*, on 



brane of the spore changes considerably, especially in its 

 upper portion. It increases in thickness, and when a section 

 is made, several layers are distinguishable. It can with 

 difficulty be stripped off from the prothallium.* When 

 viewed superficially the membrane which was previously 

 homogeneous appears finely granular — all which phenomena 

 are found to occur in a remarkably similar manner in the 

 embryo-sac of the Coniferae. 



The spherical prothallium increases in size by multiplica- 

 tion and expansion of its cells, and ruptures the upper half 

 of the exosporium, dividing it into three lobes, each of the 

 three ridges which unite at the apex of the spore separating 

 into two longitudinal halves. A small portion of the apex 

 of the prothallium — three very pointed triangles meeting at 

 anoies of 120° — is thus made free. 



Archegonia are produced by the multiplication of indivi- 

 dual cells of the upper surface of these exposed portions. 

 The first of these archegonia is produced exactly at the apex 

 of the prothallium (PI. XLVI, fig. 2). If this first one 

 remains unimpregnated several others are formed in descend- 

 ing order. I-have never counted more than eight. 



The mother-cell of an archegonium divides by a septum 

 parallel to the free outer surface, and a similar division 

 takes place in the outer of the two newly -formed cells. 

 Vertical longitudinal septa then divide each of the two 

 upper cells into longitudinal moieties (PI. XLVI, fig. 3a), 

 in each of which a longitudinal septum at right angles to 

 the one last formed is immediately produced. The under- 

 most cell of the archegonium increases somewhat in size 

 and becomes the central cell. Division by transverse septa 

 usually occurs once more in the lower of the two double 

 pairs of (four times smaller) cells which project beyond the 

 central cell (PI. XLVI, fig. 3, a 1 ). Exceptions to this are rare. 



During these processes the part of the inner membrane 

 of the spore-cell which is not- covered by the exosporium 

 peels off gradually, swelling up in front.f By the parting 

 asunder of the four longitudinal rows of cells which cover 



* Compare Mettenius, ( Bot. Zeit.,' 1848, p. 690. 



f The mode of growth of the adventitious roots of some grasses, especially 

 of Avena sativa, affords a very remarkable instance of the peeling off of whole 

 masses of cellular tissue by the casting off of the primary membrane and the 

 thickening layers of the epidermal cells. 



