36] Reproduktive Organe. 1609 



95. Nichols, G. E. A niorphological study of Juniperus communis 

 var. depressa. (Beih. Bot. Üentrbl., XXV, I.Abt., 2. H., 1910, p. 201— 241, mit 

 10 Taf. u. 4 Textfig.) 



Die Arbeit behandelt die Entwickelung der männlichen und weiblichen 

 Sporangien und Gametophyten, sowie die Befruchtung und Embryoentwicke- 

 lung. Die Ausführungen werden durch sehr zahlreiche Abbildungen erläutert. 

 Verf. faßt die Ergebnisse in folgender Weise zusammen: 



The buds which give rise to the staminate cones are lormed during the 

 Summer of the year precending pollination. 



The archesporium originates from one or more hypodermal cells at the 

 base of the sporophyll. 



The tapetum and the inner layer of the sporangium wall are both 

 derived from the outermost cells of the archesporium, while the outer layer 

 of the wall — the only layer present in the mature sporangium — is developed 

 from epidermal cells. Thus the inner layer of the wall is more closelj^ cor- 

 related to the tapetum than to the outer wall-layer. 



The microspore mother cells enter synapsis about May Ist. Präparatory 

 to this period a pairing of different portions of the chromatin becomes evident, 



At the completion of the heterotypic division two restiug daughter 

 nuclei are formed, but a wall is never developed between them. The second 

 division may be either tetrahedral or bilateral. 



Preparatory to the formation of microspores the cavity of the mother 

 cell becomes divided into four Chambers by thick, transparent walls. Within 

 these compartments the spores are developed, and they are eventually set free 

 by the breaking down of the enveloping walls. 



Pollination occurs about May 25th. 



The elapsed time between pollination and fertilization is about twelve 

 and a half months. 



During the first season's growth the pollen tube penetrates a short 

 distance into the nucellus and frequently branches, while the primary nucleus 

 divides, giving rise to the tube nucleus and the nucleus of the generative cell. 

 The latter immediately becomes surrounded by a „Hautschicht". 



Soon after the renewal of activity the foUowing spring the nucleus of 

 the generative cell divides, forming the stalk nucleus and the body cell nucleus. 

 The latter becomes invested with a definite membrane, but a true stalk cell 

 is never formed. 



By the time the pollen tube enters the archegonium Chamber the body 

 cell has attained a diameter of about 60 /n. 



The division of the body cell takes place about three days before fertili- 

 sation and usually results in the formation of two male cells equal in volunie 

 and bounded by definite membranes. The spindle of this division is of intra- 

 nuclear origin. 



Several instances were found where three or four male cells had been 

 produced by the division of one body cell, but it is probable that no more 

 than two are ever functional. 



The ovulate buds first become distinguishable from vegetative buds a 

 few weeks before pollination. 



The archesporium is derived from the cells in the lower portion of the 

 nucellus and is recognizable at the time of pollination, but it is impossible to 

 distinguish the megaspore mother cell until the following spring. 



