Guilliermond - Atkinson — 124 — Cytoplasm 



pollen of flowers produced on colorless branches. Most of the 

 descendants of such a cross are green, some are variegated but 

 none are colorless. To explain these data, the hypothesis has been 

 put forth that the oospheres and pollen grains within flowers grow- 

 ing on uncolored branches contain only plastids incapable of be- 

 coming green. In the first series of experiments, the oospheres 

 with modified plastids reached by pollen tubes with plastids equally 

 modified, give rise to colorless plants; when reached by pollen 

 tubes containing normal plastids, they produce variegated or green 

 plants because a small number of plastids of male origin have 

 penetrated the oosphere. During the succeeding divisions the 

 normal plastids are distributed by chance. When some cells re- 

 ceive only these normal plastids, while others receive modified 

 plastids of maternal origin, variegated plants are obtained. When 

 the normal plastids, although brought in in very small numbers, are 

 distributed among all cells of the embryo, an entirely green plant 

 is the result. Finally, when normal plastids, having been brought 

 in in very small numbers remain in a negligible quantity, colorless 

 plants are obtained. In the second series of experiments, colorless 

 plants were never procured because in this case the cytoplasm of 

 the oosphere, which is always in excess of that delivered by the 

 pollen tube, contains normal plastids. The few variegated seed- 

 lings give evidence of modified plastids having been brought in by 

 the pollen tube. Finally, to account fully for the differences between 

 the results obtained in the two series of experiments, it must be 

 admitted that the normal plastids, capable of becoming green, in- 

 crease in numbers more rapidly than do the modified plastids. 

 That is why the latter, although brought in in large quantity by the 

 pollen tube, are never represented exclusively in one plant. 



The hypothesis is evidently plausible but it has no cytological 

 basis — at least up to the present — for we have seen that the be- 

 havior of the plastids and chondriosomes in fertilization is not 

 known. 



