352 Mottier. — On the Prophases of the Heterotypic Mitosis . 
Overton, James B. (’05) : Ueber Reduktionsteilung in den Pollenmutterzellen einiger Dikotylen. 
Jahrb. f. wiss. Bot., xlii, 121-53, I 9°5- 
(’09) : On the organization of the nuclei in the pollen mother-cells of certain 
plants, with especial reference to the permanence of the chromosomes. Ann. of Bot., xxiii, 
19-60, 1909. 
EXPLANATION OF PLATE XXIII. 
Illustrating Professor Mottier’s paper on the prophase of the heterotypic mitosis. 
All figures were drawn from sections with the aid of the Abbd camera lucida, and with Zeiss 
apochromatic immersion 2 mm., apert. I. 40, and compensating ocular 12, excepting those showing 
outlines of ovules, 1 a, 2 a, &c., which were drawn with low powers. Magnification of figures of 
nuclei about x 1800. 
Figs. 1 a, 2 a, &c., represent outline drawings of the ovules in which the nuclei, Figs. 1,2, &c., 
respectively occur. 
Fig. 1. The nucleus of a megaspore mother-cell at an early stage in the period of growth prior 
to synapsis. In Fig. 1 a, a small piece of the ovule was cut away along the line x — x before fixing. 
Fig. 2. About the same stage in mitosis as Fig. 1. The chromatin is in form of irregular lumps 
of varying size. One large and two or more smaller nucleoli are present. In this case the wall of 
the ovary was not cut away to allow the fixing fluid direct access to the ovule. A layer of tissue 
six or seven cells in thickness must have been traversed before the fluid reached the ovule. The 
lumpy condition of the chromatin is supposed to be due in a measure to the action of the reagents. 
Fig. 3. A later stage than Fig. 1. The nuclear structure consists of a delicate network holding 
the small chromatin granules uniformly distributed. A large and two small nucleoli are present. 
Fig. 3 a shows the part of the ovule cut away before fixing. 
Fig. 4. A nuclear thread or spirem has been formed which is undergoing synaptic contraction. 
Fig. 5. Synapsis has progressed further. The spirem is a single thread, and the chromomeres 
are somewhat larger than in the preceding figure. 
Fig. 6. The stage of the dense synaptic ball. 
Fig. 7. The spirem loosening up after synapsis. The longitudinal fission, if present, is not 
visible. 
Fig. 8. The spirem is becoming distributed in the nuclear cavity. Only here and there can any 
evidence of a longitudinal fission be seen (at the right near a cut end of the thread). 
Fig. 9. The stage of the hollow spirem ; the section includes a part of the spirem only. The 
longitudinal fission is quite distinct, the segments diverging somewhat in places. 
Fig. 10. The same stage in mitosis as Fig. 9. The spirem is more slender, and the longitudinal 
segments separate for longer stretches. It is probable that the slender nature of the spirem and the 
greater divergence of the halves are due partly to the reagents. Fig. 10 a (.* — a) shows the part of 
the ovule cut away before fixing. 
Fig. 11. A later stage, at the time of the second contraction and of the looping and approxima- 
tion of different parts of the spirem to form the bivalents prior to complete cross segmentation. The 
longitudinal halves of the spirem, which frequently show a tendency to diverge more or less at an 
earlier stage, have unmistakably and beyond all question united, so that there is now a single and 
rather thick and smooth cord. At this stage, both here and in the pollen mother-cell, indications of 
the longitudinal split may occasionally be made out. Fig. 11 a will indicate the structure of the 
ovule at this stage of mitosis. 
