Beer.— Studies in Spore Development. 2 1 3 
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Bot. Centralbl., Bd. xxii, 1907, pp. 191-210. 
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t. xxxvi, 1889, p. 391. 
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pp. 163-173. 
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EXPLANATION OF PLATE XIII. 
Illustrating Mr. Beer’s paper on Spore Development. 
All figures refer to Ipomoea purpurea, Roth. , and were drawn with, the aid of the camera 
lucida. For Figs. 1, 4, 6, 8, 9, 12, 15, 16, and 18, Zeiss’ apochrom. objective inch (apert. 
1.40) and compens. oc. 8 were employed, whilst for Figs. 5, 7, 11, 13, 14, 17, 19, 20, Leitz’s inch 
object, and compens. oc. 8 were used. Magnification about 1500 and 1100 respectively. 
Fig. 1. Telophase of second meiotic division, (a), (ft), (/) show gradual vacuolization and 
dispersal of chromosome material. ( d ) Nucleus from tissue of young vascular bundle showing 
chromatic aggregates. 
Fig. 2. Young pollen-cells surrounded by special walls, x about 640. 
Fig. 3. Triradiate middle lamellae of special walls left after disintegration of this wall. 
Fig. 4. Young pollen-grain with simple exine. The special wall still encloses the pollen-grain. 
Fig. 5. Inner surface view of exine of young pollen-grain. 
Fig. 6. ( a ), ( 6 ), (c). Exine of young pollen-grain in section. Same stage as Fig. 5. 
Fig. 7. Young pollen-grain soon after its liberation from special walls. 
Fig. 8. Older stage of exine than that shown in Fig. 7. 
Fig. 9. (a) Still older stage of exine. The two prongs or roots of spine are clearly shown. 
(£) Slightly more enlarged view of spine. 
Fig. 10. Protoplast of pollen- grain reduced to a hollow shell of substance, x about 480. 
Fig. 11. Nucleus of pollen-grain in which the protoplast is just beginning to be reconstructed. 
Fig. 12. A cytoplasmic projection into one of the exit pores in the exine. Dark stained 
material is shown apparently entering the pollen-grain at this point. 
