Studies on the Binucleate Phase in the Plant-cell. 7 



is impossible to say, when a nucleus is observed in the act of 

 division, whether it will ultimately give rise to paired nuclei in a 

 single cell or to the solitary nuclei of two sister cells. It is 

 interesting to observe that the nuclei of cells which are adjacent, 

 or almost adjacent, may divide simultaneously, one giving rise to 

 paired nuclei enclosed in a phragmosphere, while the other produces 

 two nuclei whose phragmoplast deposits a new cell wall in a 

 perfectly normal fashion. 



The parenchyma cells of the pith and ground tissue are rela- 

 tively large and vacuolate, and, as usual in such cases, the wall 

 formation occurs by the " progressive " method first described by 

 Treub* — the two nuclei and the phragmoplast travelling across 

 the cell in order to carry the new cell wall over the entire area. 

 The cell figured on PL I, fig. 27, shows this point, and also illus- 

 trates the fact that a pair of free nuclei may be formed within a 

 single cell, and that one may subsequently divide into two daughter 

 nuclei which become separated by a cell wall. A similar occur- 

 rence has been described by Nemec f in the case of the multi- 

 nucleate plerome elements of Ricinus, but he mentions that it is 

 extremely rare. This wall formation between the daughters of a 

 nucleus which was itself " free " shows that the appearance of 

 binucleate cells cannot be taken to indicate that the power of 

 initiating wall formation is actually lost ; it should rather be 

 regarded as being in abeyance. 



The fact that in the stem of Asparagus wall formation is 

 actively continued to some little distance below the apex is 

 perhaps connected with the existence of a subsequent period of 

 extremely rapid cell stretching and elongation. This point may 

 be illustrated by some actual measurements. A shoot whose 

 above-ground portion was 6 "3 cm. long on May 12 increased in 

 a week to 18*3 cm., thus almost trebling its length, but remain- 

 ing unbranched. In the next week (May 19 to 26) it not only 

 increased to 84 cm. — adding, that is to say, 05*7 cm. to its stature 

 — but also threw out branches from the axils of all the upper 

 leaves; the lowest of these branches was 18 cm. long, or about as 

 tall as the entire main axis of a week ago ! Such rapid growth 

 must be very largely a matter of the elongation of already existing 

 cells, so it is not sui-prising that the Asparagus shoot prepares 

 itself by a good deal of preliminary wall formation. After this 

 great growth has taken place, and the short, thick Asparagus shoot 

 has become slender and branched, binucleate cells may still be 

 observed near the apex, showing that this character is not confined 

 to the very young stages. 



The distance from the apex at which the binucleate phase 

 begins to make its appearance was determined by means of serial 



IContd. on p. 10, 



♦ Treub, M. (1879). t N6mec, B. (1910). 



