86 McKenney — Observations on Embryo-sacs. 



He has traced almost the complete history of spindle form- 

 ation. He finds the spindle fibres to first make their appear- 

 ance as a band of kinoplasmic fibres surrounding the nucleus. 

 These later assume such a position that they radiate from the 

 nucleus in all directions. The fibres then push into the 

 nucleus, become attached to the developing chromosomes, 

 and arranged in the form of a multipolar spindle. Then the 

 fibres rearrange themselves to form the bipolar spindle. The 

 spindle fibres seem but seldom to come to a definite point at 

 the poles ; they form usually a brush-like termination. At 

 no period during the history of the spindle was Mottier able 

 to find anything resembling a centrosome. 



The writer has observed most of the stages as described by 

 Mottier during spindle formation. At no period in the cell 

 history is a centrosome visible. It seems quite likely that if 

 centrosomes are present in flowering plants, they would be 

 seen by a greater number of observers, especially when the 

 same objects and methods are employed. 



EXPLANATION OF PLATE XL 



Fig. I . Longitudinal section of apex of young ovule of Scilla hyacinthoides var. 

 earulta. p, primine fundament ; T, primary tapetal cell ; A, Archesporium. 



Fig. 2. Longitudinal section of an older ovule of Scilla hyacinthoides var. 

 carulea. p, primine fundament ; s, secundine fundament ; T, primary tapetal 

 cell ; A, Archesporium ; a, first daughter archesporial cell. 



Fig. 3. Longitudinal section of young ovule of S. hyacinthoides var. cterulea. 

 T' and T', daughter cells of primary tapetal cell. 



Fig. 4. Chain of cells resulting from division of primitive archesporium of S. 

 hyacinthoides var . carulea. A' and A', daughter cells resulting from last division 

 of the archesporium. 



Fig. 4(2. Last division or reduction division of the archesporium giving rise to 

 cells A' and A'' of Fig. 4. 



Fig. 5. Longitudinal section of ovule ot S. hyacinthoides var. ccsrulea showing 

 the binucleate daughter cells of the archesporium. A' becomes the normal 

 embryo-sac. 



Fig. 6. Chain of cells developed from primitive archesporium, S. campanulata. 

 E, Embryo-sac in quadrinucleate stage. 



Fig. 7. Mature embryo-sac with rudimentary second embryo-sac E' below, in 

 S. campanulata. 



