Nichols, A morphological study of Juniperus communis var. depressa. 213 



the wall of the spore (flgs. 40— 42). This cell is at first lenticular, 

 but toward the close of the summer it rounds out and becomes 

 spherical, thus separating more or less from the spore wall. The 

 male gametophyte passes the winter in the condition represented 

 by flg. 43. 



Activity recommences early in the spring when the tube 

 nucleus moves down toward the tip of the pollen tube (fig. 44), 

 where it becomes surrounded by a dense mass of cytoplasm. The 

 lower portion of the pollen tube now undergoes a marked increase 

 in size, enlarging in all directions at the expense of the adjacent 

 sporophytic tissue, but there is no marked growth in length until 

 after the division of the generative cell which occurs late in April. 



Fig. 45 shows the spireni of the division by which the stalk 

 and body nuclei are produced, but none of the later phases were 

 seen. The division is consummated very rapidly. Fig. 46 is drawn 

 from a pollen tube in the same pollen Chamber as that from which 

 fig. 45 is taken and represents the two resulting nuclei. The 

 smaller of the two is the nucleus of the body cell, the larger is 

 the stalk nucleus. The phenomena which follow the division of 

 the generative cell in the conifers present certain differences, as 

 described by various writers. Belajeff (1893) and Strasburger 

 (1892) report that in J. communis and Thuja respectively two 

 cells of unequal size are formed. the larger of which, the stalk 

 cell, degenerates. Coker (1903b) describes a similar condition in 

 Taxodium. In Sequow (Lawson 1904 a) and in Saxegothaea 

 (Noren 1907), on the other hand, immediately after the division 

 of the generative cell the nuclei of the stalk and body cells lie 

 free in a common cytoplasm. In Sequoia the body nucleus soon 

 becomes invested with a dense zone of cytoplasm and develops a 

 distinct membrane, but at no stage is there a distinct stalk cell. 

 The observations of the writer show that in the species studied 

 the two nuclei likewise at first lie free in the cytoplasm of the 

 tube, and that a true stalk cell is not formed. Doubtless a closer 

 examination of this phase in other Owpresseae will show similar 

 conditions. 



Very soon after their formation the stalk and body nuclei 

 pass down toward the tip of the tube, the stalk nucleus usually 

 in advance. The tube nucleus, which has meanwhile wandered 

 back toward the upper end of the tube, meets the two nuclei about 

 midway, and they pass down the tube together (fig. 47). The 

 three are easily distinguished at this period, the stalk nucleus being 

 somewhat larger than the body nucleus and slightly smaller than 

 the tube nucleus, while there is usually a similar difference in the 

 size of their nucleoli. By the time they have come to rest in the 

 swollen tip of the tube, the body nucleus has become surrounded 

 by a dense zone of cytoplasm and is cut off from the surrounding 

 protoplasm by a definite membrane (fig. 48). Concomitantly with 

 this condition in the male gametophyte, the megaspore, which has 

 begun to germinate, is in the four nucleate stage. 



