^89.] BOTANICAL GAZETTE. 



2 4* 



division the nucleus must first disappear, two new ones aris- 

 ing in its place. The nucleus occupied a secondary place as 

 a derivative organ. And the chlorophyll granules were be- 

 lieved by him and his contemporaries to be. new formations 

 irom homogeneous protoplasm under certain conditions of 

 light, temperature and food. Researches, which leave no 

 room for doubt, have shown that the nucleus, in all cases 

 hitherto examined, springs from a pre-existent nucleus bv 

 a process of division. The process of division, with its mar- 

 velous sequence of formal arrangements of definite portions 

 in meridional lines and in polar and equatorial masses, has 

 been most carefully examined in almost every organ of the 

 plant, and in connection with similar processes of cell-divis- 

 ion in animal tissues. In no well marked case has a nucleus 

 been observed to arise from homogeneous protoplasm, even 



a few doubtful instances having been lately explained satis- 

 factorily. 



The extraordinary manner in which the nucleus, both in 

 common cell-division and in reproductive blending, carries 

 ancestral characters and controls the distribution of nutri- 

 tive materials, is as vet the greatest mystery in vegetable 

 life. 



We pass next to consider a very important change of 

 view in regard to the other granules imbedded in the proto- 

 plasmic body, known as leaf-green or chlorophyll granules. 

 Formerly, as we have noticed, it was held that all of these 

 sprang by a process of differentiation from the shapeless mass 

 in each exposed cell. Researches by Schmitz on some of 

 the lower plants, and by Schimper and Meyer on the higher, 

 have shown beyond any reasonable doubt that these chloro- 

 phyll granules always arise bv a process of division from pre- 

 existent granules. But this fact, taken by itself, might not 

 possess great interest. It is, however, known that at the 

 growing points where leaves are developed, the cells contain 

 in their protoplasm granules of about the consistence and 

 color of protoplasm itself, and these granules have the power 

 of division, much after the fashion of the cell nucleus. But 

 the products of such division are essentially three-fold ; some 

 of the resulting granules are colorless, like the mother gran- 

 ules, others become true chlorophyll granules, while others 

 still, in those leaves which become the leaves of the flower 

 and the fruit, assume colors other than green. In other 

 words, we have in these associated granules, or chromato- 

 phores, a morphology which is of the highest interest. The 



