1882.] the Pollinium in Asclepias. 289 



transverse, i. e. horizontal, division likewise in the same plane. The 

 cells in consequence of this take the form of short prisms whose 

 direction is inclined obliquely downwards from the surface. Of 

 these prisms four appear in transverse section and the free faces of 

 the two lateral ones are somewhat rounded, so that the whole mass 

 has now a slightly elliptic form. Further division of each of these 

 prisms is then continued in both the longitudinal and horizontal 

 planes parallel to the long axis of the cell ; the result of which is 

 that the loculus of the anther now contains a large group of cells 

 comparatively narrow in proportion to their length, which appear in 

 any transverse section as a single row consisting of eight to twelve 

 or more cells. Seen in this view they are of extreme length, being 

 six to ten times longer than they are broad, of large size and rhom- 

 boidal or prismatic form, while they pursue a slightly oblique 

 direction ; each possesses very granular protoplasmic contents con- 

 taining a large circular nucleus with a nucleolus, a large vacuole at 

 either end, and a thin cellulose cell-wall. Their vertical or longi- 

 tudinal walls form a common partition between these cells on the 

 one hand, and the cells of the tapetal limiting membrane which 

 closely surrounds them on the other. Some of them may at a 

 slightly later period be found exhibiting two nuclei in close proximity 

 to each other. In longitudinal sections they may be seen to lie in 

 numerous obliquely directed rows arranged one above the other. 

 But all the narrow prismatic cells contained in a loculus remain 

 parallel and closely appressed together in close and intimate con- 

 nection one with another so that they cannot be separated one from 

 the other without injury and rupture ; in the relative thickness of 

 their walls moreover they present no difference which would enable 

 one to assert with any degree of certainty, when this stage has been 

 reached, that any special aggregation of cells was the direct 

 derivative of one of the segments of the primitive-mother-cell. 

 The coherent tissue completely filling the cavity of the loculus 

 bounded by the tapetal membrane, has throughout thoroughly the 

 appearance of a cell-mass all of whose cells have been repeatedly 

 bisected in succession by a series of divisions in two planes only. 



At this stage of their development they correspond exactly to 

 the contents of a single loculus in the young anther of Zostera, 

 a genus of Monocotyledons, whose mode of pollen-formation has 

 been studied in a most masterly manner by Hofmeister 1 . Indeed, 

 the earlier stages of Asclepias and those of this last-named genus 

 exhibit an extremely close correspondence with one another, the 

 only marked difference between the two being that in Zostera 

 the anther is quadrilocular. My observations up to this point 



1 loc. cit. pp. 125 — 128, plate iii, figs, i — 15b; also Ncuc Beitrage, ii., pp. 

 643—645. 



