598 APPENDIX. 



same kind : it exhibits a large cytoblast and a very evident circulation in stream- 

 lets. The pollen-cells are empty, but the parent-cells are full of a thickened 

 muco-granular (especially nitrogenised) contents. Gradually the contents of the 

 parent-cell become clear and gelatinous, whilst the four pollen-cells get filled 

 with a similar substance to that contained earlier in the parent-cells. This is 

 seen in 



Fig. 15. Parent-cells at a period the same as fig. 11. The parent-cells soon 

 become dissolved, the pollen grains begin to assume a round form, and to sepa- 

 rate the external pollen membrane. During this time the cellular tissue of the 

 anther-wall (fig. 13. b.) becomes developed and arranged. 



Fig 16. A somewhat later condition than fig. 11. The pollen grains are quite 

 completed (as fig. 17.) a, The perfectly developed epidermis ; Z>, the cell-layer, 

 in which is evident a circulation in reticulated streamlets (later spiral layers) ; c, 

 somewhat elongated cells, containing chlorophyll grains; d, cells still more elon- 

 gated, very flat, and containing opaque (nitrogenous) contents ; <?, radical, elon- 

 gated, sac-formed cells, in which a process of cell-formation is going on, and 

 which contain two free cells with large cytoblasts ; these cells are subsequently 

 entirely resorbed. 



Fig. 17. A perfectly-formed pollen grain, consisting of the essential pollen-cell 

 and a layer of secretion (the external pollen membrane). It has four circular 

 clefts, in which the pollen lies free (uncovered). 



Fig. 18. Section of the pollen-membrane, c, Essential membrane of the pollen- 

 cell ; 6, layer of secretion ; d, projections formed of the same substance, and in 

 union with the layer of secretion. It forms the reticulated united elevations on 

 the whole surface of the granule. The little pits or cavities thus formed are filled 

 with a clear, firm, gelatinous substance, a, perhaps tne residuum of the dissolved 

 parent-cells. 



What I have observed on the development of the pollen, I have here, and in the 

 text on other plants, communicated. Whether myself or Na'geli is right, or both 

 wrong, the future alone can decide. 



PLATE V. 



Development of the Seed-bud (Ovule), Stigma, and Embryo. 

 Figs. 1 3. Development of the Seed-bud in Passiflora 2'iKceps. 



Fig. 1. Three seed-buds at a period somewhat earlier than fig. 11. a, Very 

 young seed-bud, forming a simple, rather curved wart (the nucleus of the bud and 

 the stalk of the bud undistinguishable) ; b, a seed-bud further developed, in which 

 the first integument is already formed, and which embraces the base of the 

 nucleus so as to distinguish it from the peduncle of the bud (funiculus) ; 6", longi- 

 tudinal section of one in a medium condition; 1, point of the nucleus (nuclear 

 wart) ; 2, appearance of the first integument. At the point of the nucleus 

 is seen a strikingly-enlarged cell containing cytoblasts : this is the future embryo- 

 sac. 



Fig. 2. Seed-bud at a somewhat later period than fig. 11. (PI. IV.) , The 

 nucleus already covered with the first integument, 2, and this again with a second, 

 3, so that the peduncle (4) of the bud is perfectly separated j a', a similar bud 

 seen in front ; b, longitudinal section of the upper part of a somewhat further 

 developed bud, which is explained fig. 1 b f and fig. 2 a ; c, a seed-bud unfolding in 

 an abnormal way. The figures are the same as in a. The contrast is striking in 

 this case between the cells of the peduncle (4) of the bud, arranged in long rows, 

 and, on account of the air in the intercellular passages, of a black colour, and the 

 round, succulent, cellular tissue of the seed-bud. 



Fig. 3. Longitudinal section of a perfectly-developed (inverted) seed-bud before 

 impregnation, a, Peduncle of the bud ; b, external integument ; c, internal 

 integument ; d y nucleus, e, embryo-sac ; /, opening of the bud (micropyle) ; 

 g, base of the bud j 7z, raphe. 



