290 Mr Corry, On the Development of [Nov. 27, 



accord at first with the single recorded observation of Schacht 

 rather than with those of Hofmeister, though they commence at a 

 much earlier stage than was noticed by either of these writers. 

 Hofmeister regards the pollen as derived not from a single primi- 

 tive-mother-cell, as seen in tranverse section, but from a group of 

 primitive-mother-cells. Being unable to trace his 'group' of cells 

 back any farther he regards Schacht's statement and figure 1 that 

 in Asclepias only a single primary-mother-cell is formed in each 

 anther lobe as erroneous. The ultimate conclusion reached, if his 

 observations on this point be accejDted, is of course a multicellular 

 archesporium ; while my own results distinctly prove that it is 

 unicellular, and that Schacht's statement really represents the true 

 condition of the case. Apart from this, however, I have been able 

 completely to confirm Hofmeister's researches in so far as they 

 relate to the pollen-development of Asclepias up to the stage 

 at which the most obvious resemblance to that of Zostera is 

 exhibited. 



The cell-walls of the primary-mother-cell and its derivatives by 

 division are thin and always remain so, never being visibly thick- 

 ened at any subsequent period ; in this feature they resemble so 

 far as is known only Zostera and its near ally, Naias' 2 , while they 

 differ in it from the rest of Angiosperms at large. At this point 

 however, the close analogy to, and correspondence with, the type 

 of pollen-formation in Zostera ends. For in the latter the granu- 

 lar protoplasmic contents of each of these long narrow prismatic 

 cells becomes surrounded by an exceedingly thin and delicate, but 

 readily observable, cellulose membrane, and forms an elongated 

 club-shaped or fusiform pollen-grain, exhibiting therefore perhaps 

 the most primitive type of pollen formation known in the Phanero- 

 gams. In Asclepias, on the contrary, further division of each of 

 the prismatic cells takes place resulting ultimately in the for- 

 mation of the special-mother-cells of the pollen in the following 

 manner. 



Succeeding the division of the nucleus of each of the prismatic 

 cell into two parts (which feature it has been already mentioned 

 was observable in some of the cells), the protoplasmic contents 

 now divide vertically into two at right angles to the long axis 

 of the cell, and therefore in the direction of the breadth of the 

 anther and at right angles to all the previous planes of division ; 

 simultaneously the formation of a cell-wall takes place in the 

 plane of division, i. e. parallel to the short sides of the prism. 

 By means of this septum the prismatic cell becomes divided into 



1 Das Microslcop, pi. iii. fig. 8; English Edition, p. 105, fig. 21 a. 



2 W. Hofmeister, Neue Beitrage zur Kenntniss der Embrgobildung der PhancrO' 

 gamen, part ii., Monokotglcdoncn, pp. 642 — 043, plate i., figs. 1 — 12, 1859. 



