Higher Cryptogamia and the Phanerogamia. 451 



weeks in the Abietinese ; in Pinus sylvestris and others the pol- 

 len-tubes are not produced till still later. 



At this time the embryo-sac is a simple cell ; but shortly after, 

 numerous free cell-nuclei appear in its cavity, and it soon be- 

 comes filled up with cellular tissue, which goes on increasing in 

 those Abietinea? which require two years to ripen their seeds, till 

 the following winter season ; the cells of the nucleus are much 

 multiplied meanwhile. In March and April of the following 

 year the endosperm-cells multiply still more, and by absorption 

 of the walls of the parent-cells are set free, while the embryo-sac 

 inclosing them grows to more than twenty times its former size. 

 These cells become applied in layers to the walls of the embryo- 

 sac, until it at length again appears filled with cellular tissue 

 (PI. XVII. E. fig. 2 b). After the embryo -sac has become filled 

 with cellular tissue, certain of the cells at the micropyle end of 

 it become larger than the rest, and grow into large cells (the 

 cnrpuscula) (E. fig. 3 c?). Each of these corpuscles is separated 

 originally from the surface of the embryo- sac by a simple cell; 

 this latter divides into four by two vertical septa crossing each 

 other, and then an intercellular passage is formed between their 

 inner angles leading down to the corpuscle (E. fig. 4 c). 



The number of corpuscles is from three to five in Pinus syl- 

 vestris and austriaca ; mostly three in Abies balsamea and pecti- 

 nata ; generally four (rarely five) in Pinus canadensis ; and five 

 to eight in Taxus and Juniper us. 



Free cells are next produced in the cavity of each corpuscle 

 (E. fig. 4, 5 d) ; some of them usually appear as it were pressed 

 against the upper end, and usually one at the lower end (E. fig. of). 

 About the time the corpuscles become evident the pollen-tubes 

 resume their growth, advancing by breaking down the tissue of 

 the nucleus until they come in contact with the outside of the 

 embryo-sac, one over each corpuscle (E. fig. 3 c), while they per- 

 forate the membrane of the embryo-sac to come into the canal 

 leading between the four cells down to the outside of the cor- 

 puscle, with which they finally come in contact (E. fig. 5 e). Very 

 soon after this, the cell at the lower end of the corpuscle (the em- 

 bryonal vesicle) becomes greatly enlarged. In this a free cell is 

 found (E. fig. 6/) which divides by a vertical septum into two 

 collateral halves (fig. 7), and then by another vertical septum at 

 right angles into four elongated cells ; these are each divided by 

 a cross-wall, so that this cellular body (the proembryo) consists 

 of a short cylinder composed of eight cells. The four lower cells 

 elongate and become divided again by cross walls (fig. 8, 9) ; and 

 as the side walls of the upper cells are adherent to the walls of 

 the corpuscle, the growth causes the lower end of the corpuscle to 

 be pushed downwards; finally this gives way, while the cells of 



