Kichols, A morphological study of Juniperus communis var. depressa. 223 



which, the exosporium, is fibrillar and somewhat thicker than the 

 inner, homogeneous endosporium. According to Thomson the exo- 

 sporium is suberized, while the endosporium is composed principally 

 of cellulose. When viewed from its outer surface the membrane 

 presents a speckled appearance, and this in Taxodium led Coker 

 (1903b) to conclude that the coat was pitted. Thomson, however, 

 shows that pits are not present. 



Just as the megaspore membrane is homologous with the 

 coat of the microspore, the so-called "spongy tissue" is now 

 generally recognized to bear the same relation, on morphological 

 as well as physiological grounds, to the tapetum of the micro- 

 sporangium. Thomson (1905 a) finds that in Gymnosperms "where 

 the normal type of membrane occurs, there is present a more or 

 less well defined tapetum". Noren (1907) describes this tissue in 

 J. communis, and its history in var. depressa will be only briefly 

 referred to here. As in the mierosporangium the tapetum is de- 

 rived from the non-functional cells of the archesporium. At the 

 time of the tetrad division these cells are large and readily dis- 

 tinguishable from the surrounding nucellar tissue (fig. 62). They 

 have large nuclei and are densely packe d with cytoplasm in which 

 are imbedded minute starch granules. As the megaspore develops 

 the cells of the tapetum divide actively and continue to invest the 

 young embryo sac (fig. 71). The layer is still present when 

 the cellular tissue of the prothallium is being organized (fig. 74), 

 but after this it rapidly disorganizes. 



The archegonium. — According to Noren (1907) the 

 archegonia are derived from the superficial cells in the upper part 

 of the prothallium. The nucleus of the archegODium initial soon 

 clivides, cutting off a primary neck cell which by subsequent di- 

 visions forms usually a Single tier of four neck cells. The arche- 

 gonia vary in number from four to ten, and, as is characteristic 

 of the Cupresseae, they are always grouped close together without 

 intervening parenchyma, thus forming a Single complex. During 

 the development of the archegonia to their füll size the vegetative 

 cells at the upper end of the endosperm grow and divide rapidly, 

 and as a result of this local activity the prothallial tissue surround- 

 ing the archegonium complex rises above the level of the neck 

 cells, a depression in the tip of the prothallium being produced at 

 the bottom of which lie the archegonia. 



Fig. 78 of the present paper represents the archegonium 

 Chamber in var. depressa in the process of formation. At this 

 stage, which is found about one week before fertilization, the 

 central cell of the archegonium contains a relatively small amount 

 of cytoplasm restricted to the periphery of the cell, thus enclosing 

 a large central vacuole. The nucleus lies directly beneath the 

 neck cells, and, while at first it scarcely differs from those in the 

 surrounding prothallial cells, it soon becomes distinguishable by its 

 large size. 



Shortly before the division of the central cell nucleus to 

 form the ventral canal nucleus and egg nucleus the cytoplasm of 



