136 INTRODUCTION TO CYTOLOGY 



the distribution of the cells containing it, and (3) combinations of colored 

 sap with chloro- and chromoplasts." Autumnal coloring is due to the 

 formation of pigments as disorganization products: when cytoplasm and 

 chlorophyll are the main disorganizing substances a yellowish color results, 

 whereas if sugars are present in considerable amounts in the cell sap the 

 brighter pigments are formed. 



Extruded Chromatin. 1 — The actual extrusion of chromatin from the 

 nucleus into the cytoplasm has been reported in a number of instances: 

 in the microsporocytes of various angiosperms by Digby (1909, 1911, 

 1914), Derschau (1908, 1914), West and Lechmere (1915), and others; 

 in ferns by Farmer and Digby (1910); and in the Ascomycete Helvella 

 crispa by Carruthers (1911). The extruded chromatin commonly takes 

 the form of deeply staining globules or irregular masses in the cytoplasm; 

 often a clear area suggesting a nuclear vesicle is present about them. In 

 some cases, such as Gallonia candicans (Digby 1909) and Lilium candidum 

 (West and Lechmere 1915), the chromatin may pass through the wall 

 into an adjacent cell, where it forms a rounded mass connected by a 

 chromatic strand with the nucleus from which it originated. 



The significance of this phenomenon is by no means apparent. It is 

 not at all unlikely that nutritive materials passing from nucleus to cyto- 

 plasm during the normal metabolism of the cell occur at times as visible 

 globules at the nuclear surface. The extrusion of chromatin into neigh- 

 boring cells, on the other hand, in many cases has every appearance of 

 a phenomenon associated with degeneration or some other abnormal 

 physiological condition. West and Lechmere, however, view the process 

 as one which occurs normally at certain stages, and which will probably 

 be found to be more general in plants. Sakamura's (1920) extensive 

 researches on chloralized cells have led him to regard the extrusion of 

 large masses of chromatin as an abnormal phenomenon which occurs as a 

 result of a disturbance of the metabolism of the cell. Its more frequent 

 occurrence in sporocytes than in other cells is attributed to the unusual 

 sensitiveness of the former to disturbing influences. 



The Senescence of the Cell. — The accumulation of products of 

 metabolism ("differentiation products") has a direct bearing on the 

 problem of protoplasmic senility. As its life progresses the cell gradually 

 "ages, " and if nothing occurs to prevent it the process eventually term- 

 inates in death. What shall be taken as an index of the degree of senes- 

 cence has been the subject of much discussion. We have already called 

 attention to the attempts which have been made to correlate senescence 

 with a progressive change in the nucleoplasmic relation, concluding 

 that no constant correlation of the kind has been shown to exist (p. 63). 



Child (1915) has brought forward much evidence to show that the 



1 Extruded chromatin is not metaplasm, but it has been found convenient to 

 treat it at this point along with other inclusions of the cytoplasm. 



