CONIFERJE. 



521 



to a section of a young sporangium of Lycopodiwn : the archesporium consists 

 in both cases of a group of cells bounded by a tapetal layer. There is reason, 

 inasmuch as their mode of development is the same, to regard these cells in the 

 Cupressineae as being, like the archesporial cells of Lycopodi'ufn, spore-mother-cells ; 

 but whereas in Lycopodium each of these mother-cells produces four spores, in 

 the Cupressineae only one of them persists and it produces only one spore, the 

 embryo-sac. The embryo-sac is then the equivalent of the macrospore of the 

 heterosporous Vascular Cryptogams. 



In the Abietinese, the archesporium has become much reduced as compared 

 with that of the Cupressineae. The Cupressineae resemble the higher Vascular 

 Cryptogams in the mode of development of the ovule and embryo-sac, whereas the 

 Abietineae approach the Angiosperms.] 



Develop7neni of the Endosperm (Prothallium). The first stage in the development 

 of the endosperm is the division of the nucleus of the embryo-sac ; each of the two 

 nuclei divides again, and this process is repeated until a number of nuclei have been 

 formed which lie in the peripheral protoplasm. Around each nucleus the protoplasm 

 becomes marked off by an ectoplasmic layer, cell-walls are formed, and thus one 

 or two layers of endosperm-cells are formed in the embryo-sac in contact with its 

 wall. These cells grow in the radial direction, and divide in such a manner that 

 the embryo-sac is filled with parenchymatous tissue. In those Coniferae in which 

 the seeds take two years to ripen, as Pinus sylvestris and Juniperus communis^ 

 the endosperm formed in the first summer is again absorbed in the spring, the 

 protoplasm of the primary endosperm-cells is set free by the deliquescence of their 

 cell-walls, and forms by division a number of new cells which, in May of the second 

 year, again fill with parenchymatous tissue the embryo-sac now considerably in- 

 creased in size. 



The archegonia (corpuscula) are developed, according to Strasburger's obser- 

 vations, from superficial cells of the prothallium (endosperm) in the same manner 

 as the archegonia of the highest Cryptogams. The mother-cell increases in size 

 and is divided by a septum parallel to the surface of the investing embryo-sac ; 

 a large inner (lower) cell is thus formed, the central cell of the archegonium, and 

 an upper small one, lying next the embryo-sac from which the neck of the 

 archegonium is formed^. In Abies canadensis this neck remains simple and uni- 

 cellular, and elongates considerably with the increase in size of the surrounding 

 endosperm ; but usually the original cell which constitutes the neck divides into 

 several cells which either lie only in one plane (Figs. 354 A, d, 355 /, d\ the 

 ' stigmatic cells,' or form several layers lying one over another (as in Abies excelsa 

 and Pinus Pinaster). Seen from above the neck appears to form a four-celled, 

 or, in Abies excelsa, even an eight-celled rosette. The homology of the ' corpus- 

 culum' with the archegonium of Vascular Cryptogams, already established by the 

 earlier investigations of Hofmeister, is carried a step further by Strasburger, who 

 discovered the formation also of a canal-cell. He considers that the part of the 

 protoplasmic contents of the large central cell which lies immediately beneath the 



^ Hofmeister (Vergleichende Untersuchungen, p. 129) gives a somewhat different account of the 

 origin of the archegonium [Germination, &c., p. 410]. 



