H 2 The Botanical Gazette. t Ma y> 



> 



methods than have been heretofore used, might perhaps 

 throw more light upon the affinities of these groups of plants, 

 or add something toward the confirmation of the generally 

 accepted views. 



As is well known, the commonly accepted view of botanists 

 is that growth in the thallus in the Marchantiaceae and allied 

 forms takes place by means of several initial cells. * From 

 careful serial microtome sections of young plants grown from 

 gemmae of Marchantia polymorpha it seems very probable that 

 in these young plants there is only one apical cell. In a 

 series of longitudinal vertical sections of a number of young 

 plants only one apical cell was found (fig. 1). Sections made 

 parallel to the surface (longitudinal transverse) of plants of 

 the same size and age as those just mentioned show two or 

 three cells lying side by side, which have been regarded as 

 initial cells, and may yet be so regarded. Kny (Hau und 

 Kntwickelung von Marchantia polymorpha, p. 374) says: "At 

 the bottom of the apical indentation, slightly bent toward the 

 under side, there is a row of cells each of which is bounded 

 externajly by a free, slightly curved wall and has two side 

 walls converging slightly toward the front and two posterior 

 meeting the latter at right angles and cutting each other at 



j^w-j a.iu >-"i-iiii S 



the back (nach ruckwiirts). [That is, the apical cell is in the 

 shape of a broad wedge]. Although one or two cells neces- 

 sarily occupy a middle position within the row, we cannot 

 therefore speak positively of two or more apical cells, because 

 it is not possible to demonstrate that a certain one or two 

 cells form the permanent organic middle point from which 

 regular segments are derived. The possibility is not excluded 

 that by further growth in width on one side of the apical re- 

 gion, one cell, at first exactly in the middle, or its axial de- 

 scendants, may be pushed to one side." Xow from sections 

 parallel to the surface of a young plant of Marchantia poly- 

 morpha (fig. 2) it is difficult to say whether cells x, x\ and 

 x'\ are all apical cells or just one, x. From the statement of 

 Kny just quoted I am rather inclined to think that one cell 

 x, is the true apical cell, and x J and x" are segments just cut 

 off in the order indicated. From fig. 3, a similar section of 

 the thallus of Asterella ham 'spine rtca, it is seen that very 

 much the same order exists, it being difficult, if not impos- 

 sible, to decide whether one, x, is the apical cell and x' and 



» - 



i Schenk: Handbuch. vol- «331. 1882. lli^£l^ 

 die Lubermoose, part (>, p. 2. 1878. Also: part 4, p. 1(5. 



