244« Dr. Schleiden oti the Development of the 



into the micropyle penetrates the intercellular passages of the 

 micleus and reaches the embryo-sac, which being forced for- 

 wards presses it, indents it, and forms the cylindrical bag, which 

 has already been described, in the commencement of this paper, 

 as constituting the embryo in the first stage of its development, 

 which consequently consists solely of a cell of leaf parenchyma 

 supported upon the summit of the axis. It is therefore formed 

 of a double membrane (excepting the open radicular end), viz. 

 the indented embryo-sac and the membrane of the pollen tube 

 itself (fig. 12, 13.). I can fi:om direct investigation refer for 

 corroboration of this fact to the following species: Taxus^ 

 Abies, Juniperus, Lathrcea, Phormium tenax, Canna Sellomi, 

 (Enothera crassipes, Mirahilis longiflora and Jalappa, Veronica 

 serpyllifolia, Limnanthes Douglasii, and less evidently in Mar- 

 tynia diandra and Cynanchum nigrum ; on the other hand most 

 beautifully clear in Orchis Morio and latifolia. In all these 

 plants I have observed the entrance of the pollen-tube into the 

 embryo-sac and the gradual conversion of its end directly 

 into the embryo ; and in Taxus, and very easily in Orchis, 

 I was even able to withdraw that portion of the tube which 

 represented the first stage of the embryo out of the embryo- 

 sac and that indeed at a tolerably advanced period*. 



The tracing of the pollen-tube into the interior of the em- 

 bryo-sac is not so easy in all plants, because the cells of the nu- 

 cleus which are arranged around the summit of the embryo- 

 sac are very firm and opake, so that it and the pollen-tube 

 cannot be exhibited quite free. In these cases, however, three 

 circumstances speak for the identity of the embryo with the 

 pollen-tube: 1st, the constantly equal diameter of the latter 

 exterior to the embryo-sac and of the former just within 

 it. 2nd, The invariable chemical similarity of their con- 

 tents shown by the reactions produced on the application of 

 water, oil of sweet almonds, iodine, sulphuric acid, and alka- 

 lies. The general contents of the grain of pollen granule is 

 starch ; and this either proceeds unchanged downwards 

 through the pollen-tube or else passes along, being previously 

 changed by a chemico-vital process into a transparent and 

 colourless fluid, which becomes gradually more and more 

 opake and is coagulable by the application of alcohol : out of 

 this, by an organizing process, the cells are formed which fill 

 the end of the pollen- tube, extending in Orchis Morio far be- 



latter of which the genus Cynanchum especially belongs. In the summer 

 of 1835 1 found Cynanchum nigrum etfuscatum to contain from two to five 

 embryos in at least every third seed. 



[♦ Onr readers are requested to refer to p. 276 for a note omitted in the 

 translation. — Edit.] 



