Nichols, A morphological study of Jimiperus communis var. depressa. 209 



They possess a rather coarse reticulum and have a distinct nucle- 

 olus. The development of resting nuclei at the close of the hetero- 

 typic division has been described in Larix (Strasburger 1900), 

 Taxodium (Coker 1903b), Pinus (Ferguson 1904), Juniperus 

 (Noren 1907), and Thuja (Lewis 1908). 



During the telophase (fig. 30) the spindle fibers are con- 

 spicuous as a barrel-shaped niass extending between the two daughter 

 nuclei, and in many cases thickenings of the fibers in the equatorial 

 plane give indications of an ephemeral cell plate, such as occurs 

 in Larix (Strasburger 1895), and occasionally in Pinus (Fer- 

 guson 1904). Coker (1903 b) reports that in Taxodium a cell 

 plate is produced which extends entirely across the cell and persists 

 throughout the second division. In Juniperus, however, the cell 

 plate entirely disappears before the initiation of the homotypic 

 division. 



In the brief period of rest which succeeds the heterotypic 

 division the daughter nuclei grow considerably in size, but within 

 a short time the flner meshes of the reticulum are again drawn in, 

 and a coarse, more or less anastomosing structure is produced 

 which gives rise to the chromosomes of the homotypic division. 

 If a spirem is formed, it is poorly defined and irregulär. The 

 spindles of the first division now disappear, new spindles are formed, 

 and the nuclear membrane is .lost sight of. As in the previous 

 division, the chromosomes become oriented at the equator (fig. 32), 

 longitudinal Splitting takes place, and the granddaughter chromo- 

 somes are drawn toward their respective poles (figs. 33, 34) where 

 the Organization of the granddaughter nuclei is brought about. 

 The nuclei thus formed are at first very small — about 7 u in 

 diameter — with a reticulum consisting of granulär masses of 

 chromatin united by finer Strands. 



As noted by Coulter and Chamberlain (1901) in Pinus, 

 the division just described may be either tetrahedral or bilateral 

 (figs. 33, 34). The former method is more prevalent, but bilateral 

 division is of frequent occurence. The successive development of 

 different microspore mother cells in the same sporangium, observed 

 by these authors and others in various conifers, is very noticeable 

 in Juniperus, especially during the stages intervening between 

 synapsis and the formation of tetrads where one step follows another 

 with comparative rapidity (fig. 11). The sporangia at the apex 

 of a cone are invariably further along in their development than 

 those at the base. 



Development of the microspores. — Miss Ferguson 

 (1904) has made some very interesting observations in connection 

 with the formation of the microspores in Pinus. She finds that 

 "the wall of the microspore mother-cell increases markedly in 

 thickness, and its protoplasmic contents is separated into four com- 

 partments by prominent cross walls which are continuous with the 

 inner portion of the mother-wall. The microspores are then de- 

 veloped, each in its own particular Chamber of the mother-cell." 

 Noren (1907) reports that in J. communis a division of the 



Beihefte Bot. Centralbl. Bd. XXV. Abt. I. Heft 2. 14 



