Nijchols, A morphological study of Juniperus communis var. depressa. 233 



The inicrospore inother cells enter synapsis about May 1 st . 

 Preparatory to this period a pairing of different portions of the 

 chromatm becomes evident. 



At the completion of the heterotypic division two resting 

 danghter nuclei are formed, but a wall is never developed be- 

 tween 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 bythe breaking down 

 of the enveloping walls. 



Pollination occurs about May 25 th . 



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 following 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 jli. 



The division of the body cell takes place about three days 

 before fertilization and usually results in the formation of two male 

 cells equal in volume and boundecl 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 prob- 

 able 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. 



Generally only one of the archesporial cells becomes a true 

 mother cell, but occasionally as many as three may function as 

 such. The non-functional cells give rise to the tapetum. 



Tetrad formation takes place late in April. As a rule but 

 one of the nuclei resulting from the heterotypic division undergoes 

 the homotypic division. 



The nucleus of the functional megaspQre becomes separated 

 from the other nuclei in the mother cell by a membrane. 



The development of the female gametophyte occupies about 

 six weeks. ' 



The megaspore membrane consists of two distinct layers. 



