34 SCIENCE PROGRESS. 



new rootlets can only be developed from cells which still 

 retain, or can re-awaken, embryonic characteristics. Be- 

 hind the region in which lateral roots arise, the cells of 

 the pericycle lose their cyanophil nature, and here again 

 the loss is first apparent in those cells from which, even 

 normally, no roots would originate, viz., those situated 

 opposite the phloem. It would be interesting to know 

 whether in the case of those roots in which the lateral 

 rootlets arise right and left of the protoxylem (e.g., Cruci- 

 ferse) a corresponding difference obtains. 



Again, Zacharias noticed that during the development 

 of the guard-cells of the stomata in a number of leaves 

 a similar difference held good. In a simple case, e.g., 

 many Liliacese, the mother-cell of the guard-cells is cut 

 off from a cell which is destined at once to form one of the 

 ordinary and relatively large epidermal cells. In this case, 

 whilst the nucleus of the mother-cell of the stoma retains 

 its nuclein contents, the other one rapidly becomes poorer 

 in this constituent, it grows and develops a large nucleolus. 

 The small mother-cell again divides to form the guard-cells 

 of the stoma, and only then does a nucleolus become at all 

 conspicuous, and the nuclein diminish in quantity. And 

 therewith the further capacity for division ceases. 



Besides the connection which is shown to exist between 

 a nucleus which is capable of division, and its richness in 

 nuclein, there are certain other facts of importance which 

 demand notice. The nuclei of cells which are actively 

 dividing are commonly characterised by the possession of 

 smaller nucleoli than are those in which no further divisions 

 will take place, but which are still growing in size. In fact 

 Zacharias states generally that, as regards nuclei of cells 

 emerging from the meristem region, the nucleoli first 

 increase to a maximum, that this is accompanied by an 

 enlargement of the nucleus as a whole, which however only 

 reaches its maximum size after the nucleolus has done so, 

 and that the latter body then diminishes faster than does 

 the nucleus as a whole. 



Further, Zacharias found that not only is the nucleolus 

 losing substance in those cells which are specialising to 



