520 PHANEROGAMS. 



The Ovules (macrosporangia), as we have already seen, are in the Podocarpeae 

 anatropous and furnished with two integuments ; in the rest of Coniferae they are 

 orthotropous and possess only one integument ; in the Cupressineae and Taxineae 

 they are erect, in the Abietineae inverted, with the micropyle towards the base of 

 the scale, to which the ovules are usually attached on one side. In these cases 

 there is no funiculus, and the ovule consists only of the small-celled nucellus and 

 one integument, which usually projects above it and forms a comparatively wide 

 and long micropylar canal, through which the pollen-grains reach the apex of 

 the nucellus, which is sometimes depressed (see Figs. 347, 348, 349, 352). Lateral 

 outgrowths of the integument not unfrequently cause the ovule, and afterwards 

 the seed, to appear winged on both sides, as in Callitris quadrivalvis (Fig. 352), 

 Frenela, &c. The wing-like appendage of the seed of Pinus and Abies, on the 

 other hand, is the result of the detaching of a plate of tissue from the seminiferous 

 scale, which remains attached lo the ripe seed. 



[The Development 0/ the Ovule and 0/ the Embryo-sac. The development of the 

 ovule begins in Taxus (according to Strasburger, Angiospermen und Gymno- 

 spermen) with the division, parallel to the surface (periclinal), of a group of hypo- 

 dermal cells at the punctum vegetationis of a lateral branch, and this is followed by 

 similar divisions in the overlying epidermis. The rudiment of the ovule is sur- 

 rounded by a projecting ring of tissue, also developed by the division of hypodermal 

 cells, which is the first indication of the integument. The ovule elongates in 

 consequence of growth and repeated cell-divisions, and consists internally of a 

 number of longitudinal rows of cells, which have all been derived from the hypo- 

 dermal layer, invested by several layers of cells which have been derived from the 

 epidermal layer. The apical cells of these internal rows are distinguished by their 

 size and by the granularity of their protoplasm ; they constitute the archesporium : 

 they are surrounded by tapetal cells, but it is not clear whether the tapetum is 

 derived from the archesporium or from the surrounding cells of the nucellus. One, 

 but sometimes more, of the archesporial cells, usually the central one, divides so as 

 to form three cells lying one above the other, and it is the lowest of these which 

 enlarges and becomes the embryo-sac. The development of the ovule in Ginkgo 

 hiloba and in Podocarpus chinensis follows essentially the same course, as does also 

 that of Thuja occidenialis. It will be observed that in these plants several embryo- 

 sacs are frequently indicated at first, but only one attains perfect development. 



In the Abietinese [Larix europcEa, Pinus sylvestris and Pumilio) the multipli- 

 cation of cells by the repeated division of the hypodermal and epidermal cells is 

 much less considerable. The archesporium is unicellular; as it elongates a small 

 cell is cut off from it towards the free surface of the ovule, which is a tapetal cell ; 

 the lower cell now divides into two, and of these two the upper divides again into 

 two ; the lowest of these three cells developes into the embryo-sac. Only one 

 embryo-sac is ever indicated in the group. 



A section of the young ovule of one of the Cupressineae, before the embryo- 

 sac is developed, presents, as Goebel has pointed out, a considerable similarity 



the Conifers are really gymnospermous. In his most recent work on the subject (Die Angiospermen 

 und die Gymnospermen) Strasburger accepts the view of the gymnospermous nature of the ovule.] 



