Higher Cryptogamia and the Phanerogamia. 453 



may say that these plants undergo all their metamorphoses 

 within the ovary, and are separated from the parent as rudi- 

 mentary perfect plants. 



In the Gymnosperms, the Conifers and the Cycads, the con- 

 ditions are more complicated. The carpels being open here, the 

 ovules are exposed and the pollen-grains come immediately to 

 the micropyle of the ovules instead of to a stigma; and the 

 pollen-tubes have to traverse only the substance of the nucleus 

 to reach the embryo- sac. But while the external conditions are 

 thus simple, those of the embryo-sac are much more complicated. 

 The endospermous cellular tissue formed within it becomes a 

 mass filling up its cavity, and on the upper. end of this appear 

 several structures, the corpuscles, presenting the most striking 

 resemblance to the archegonia of Selaginella, &c, consisting of 

 an enlarged cell crowned by four cells, leaving an intercellular 

 canal between them running down to the large cell. A pollen- 

 tube makes its way to, and passes down each of these canals, to 

 fertilize the central cell of each corpuscle : just as Suminski and 

 De Mercklin describe a spermatozoid to pass down the canal of 

 the archegonium of the Ferns. The central cell then produces 

 four suspensors, at the end of each of which a rudimentary em- 

 bryo presents itself* — only one becoming fully developed. The 

 growth of these suspensors down from the central cell of the ar- 

 chegonium or corpuscle is precisely analogous to the growth of the 

 suspensor, producing the embryo at its extremity, in Selaginella 

 and Isoetes. 



The relations to the higher flowering plants are here clear 

 enough ; the difference existing only in the superaddition of all 

 the stages of development of the endospermous tissue between 

 the entrance of the pollen-tubes and the development of the em- 

 bryonal vesicles into the corpuscles, the central cells of which are 

 physiological analogues of the embryo- sac of the higher Phanero- 

 gamia ; while the embryo-sac itself is the morphological analogue. 

 The relations to the lower plants are more diversified ; they are 

 closest in the cases of Selaginella and Isoetes, which is the more 

 interesting on account of the many other affinities between the 

 Conifera? and Lycopodiaceae. The large spore of Selaginella is 

 analogous to the ovule of a Gymnosperm, its internal coat to the 

 embryo-sac. The cellular prothollium, which is developed at the 

 summit of the cavity of the large spore of Selaginella, represents 

 the endospermous tissue of the Gymnosperm, and the archegonia 

 of the former are recognized in the corpuscles of the latter. 

 Thus, as in these corpuscles, cells become developed so as to 



* This resembles the budding of several leafy stems from the Moss- 

 spore. 



