GFMNOSPERMA E. CONIFER A E. 



337 



the definitive nucleus, the germ-nucleus, which results from the coalescence of the 

 sperm-nucleus with the nucleus of the oosphere, moves into the part of the oospore 

 which is opposite to the neck (Fig-. 260 V), and here the formation of the pro-embryo 

 begins. The small lower part of the oospore (Fig. 262 I et) which is to develope into 

 the pro-embryo and contains the germ-nucleus is either at once divided off from the 

 upper and larger part, or this does not take place till the nucleus has divided several 

 times and cells have formed round the daughter-nuclei *. 



The forma/ion of the embryo varies to a remarkable extent in the different 

 divisions ; but in all of them the considerable elongation of certain cells of the 

 suspensor thrusts the rudimentary embryo at its apex out of the oospore of the 

 archegonium into the prothallium, where the embryo proceeds to develope. 



In the Cupressineae the lower third of the oospore (Fig. 262 //) divides into 

 three cells lying one above another ; in Thuja occidentalis the two upper only of these 

 cells, which are towards the neck of the archegonium, divide each into four cells, while 

 the lower one becomes the apical cell of the young embryo. By the elongation of the 

 upper cells forming the suspensor the rudiment of the embryo is thrust forth from the 

 archegonium into the prothallium. In this case therefore each archegonium forms 

 only one embryo, which grows at first with a two-sided apical cell, but this soon 

 disappears. In Juniperus on the other hand the lowest of the three cells which lie 

 above one another divides by intersecting longitudinal walls into four cells, which are 

 pushed out by the elongation of the upper ones, round themselves off and separate 

 from one another, and each gives rise- to a rudimentary embryo ; in this case therefore 

 four rudimentary embryos proceed from one archegonium, but one only developes 

 into a perfect embryo. The commencement of the formation of the embryo is 

 different in the Abietineae (Fig. 260 F7/-AY7). The germ-nucleus moves to the 

 bottom of the oospore, and by its division forms two and then four nuclei, and four 

 cells lying in a transverse plane beside one another are formed by the accumulation 

 of protoplasm round these nuclei. The four cells divide by transverse walls into 

 three tiers one above the other ; the cells of the second tier develope into very long 

 and sinuous tubes, while those of the upper tier form a rosette which remains fixed in 

 the archegonium. The four cells of the lowest tier, which have been thrust out into 

 the endosperm by the elongation of the cells above them, divide repeatedly and so 

 contribute to the elongation of the suspensor ; then the four rows of cells of the 

 suspensor separate from one another, each bearing a terminal cell, which forms the 

 rudiment of the embryo in such a manner as to preclude from the first the existence 

 of an apical cell 2 . Thus in the Abietineae also each archegonium gives birth to four 

 rudimentary embryos; but Picea vulgar is agrees with Juniperus, inasmuch as the 

 lowest of the three primary cells of the suspensor does not divide but forms only one 

 rudiment. In Taxus baccata the embryonic structure consists of two or three tiers, the 

 upper one of which elongates and forms the tubular cells of the suspensor ; the lower 

 tier consists of from four to six cells, but only one of them ultimately produces the 



1 [See Goroschankin, Ueber d. Befr. Process b. Finns Pumilio, 1883. Strasburger, Neue Unters. 

 ii. d. Befruchtungsvorg. b. d. Phanerog. 1884.] 



2 Pinus strobus forms an exception, in which the rudimentary embryo grows by an apical cell, 

 as in the Cupressineae ; but according to modern views on the relationship of growth to cell- 

 formation this is not a matter of serious importance. 



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