43-4 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the embryo-sac. Although this cell has the appearance of being situated 

 beneath the epidermal cell, it is in reality the upper cell of the axial row. 

 At a later period this median cell has two nuclei, preliminary to a complete 

 septation and the separation of the epidermal cell, which then divides by 

 a septum perpendicular to the free surface. 



Oogenesis in Abies pectinata.*— Dr. F. Cavara gives the following 

 account of his researches on this subject. There are generally formed 

 in the endosperm two or three corpuscles, rarely only one, still less often 

 more than three. In each corpuscle is an archegonial neck, composed 

 of a few layers of quadratic cells, between which is a narrow canal. 

 At the base of the neck is the ventral cell, funnel-shaped, and separated 

 from the corpuscle by a somewhat oblique and sinuous wall. The cor- 

 puscle or archegone is large and variable in form, and is separated from 

 the surrounding endosperm by a well-defined layer of investing cells. 

 In the primordial stage of the archegone a cytoplasm is distinguishable 

 ■and a central areole corresponding to the nucleus. The cytoplasm is 

 distinguished by quite peculiar characters found in all the Abietineas 

 and probably in all the Conifer®. It is coarsely granular, and usually 

 contains a number of the formations called by Hofmeister " germinal 

 vesicles," and which Arnoldi considers to be of nuclear origin. In the 

 species under consideration they vary in size and in structure. The 

 central areole does not possess the morphological characters of a nucleus. 

 It remains for a long time in the archegone, and has no nuclear membrane, 

 linin network, or nucleoles. 



When the pollen-tube, with one of the generative nuclei, enters the 

 ventral cell, a differentiation is apparent in the oosphere, consisting 

 apparently in the expulsion or quantitative reduction of a portion of the 

 chromatic substance, with the formation of a true nuclear substance. The 

 anterior generative nucleus then passes through the thin membrane of 

 the canal, and enters the oosphere ; the posterior nucleus either remains 

 outside the ventral cell or also passes into the archegone. The union of 

 the two sexual nuclei takes place, therefore, in Abies pectinata, in the 

 prophase or in the commencement of the spireme stage. No struc- 

 tures were observed which could rightly be called centrospheres or 

 centrosomes. 



Gametophyte and Embryo of Taxodium.f — W. C. Coker finds the 

 process of formation of these structures in Taxodium distichum to agree 

 closely with those in Cupressineas, and to differ widely from those in 

 Sequoia.^ The archespore lies at the very bottom of the nucellus, and 

 resembles, in form and position, that of Juniperus, Callitris, and other 

 Cupressineaa. One of the cells at or near the centre of the group begins 

 to enlarge, and later on the megaspore extends nearly the whole length 

 of the much-enlarged nucellus. A cellular endosperm soon begins to 

 form, its growth being most rapid at the micropylar end. After the 

 endosperm has become a compact tissue, the nuclei begin to divide, 

 apparently amitotically. After the neck-cells are cut off from the 

 mother-cells of the archegones, they divide into four, as in Juniperus. 



* Bull. Soc. Bot. Ital., 1900, pp. 317-22. 



t Johns Hopkins Univ. Circulars, xix. (1900) pp. 45-6. 



X Cf. this Journal, 189G, p. 047. 



