92 



F 



DuGGAR : Development of the Pollen Grain 



{Diospy 

 Acanth 



My 



(Badula), Solanaceae 



^/ 



{Thunbcrgia), Asclepiadaccae [Gonolobiis), and Com- 

 topliord). 



v'd). It is evident that he noted the absence of 

 such fibrous tissue in Bignonia, for he briefly refers to the large 

 cells of the epidermis (see Fig. ii) as doubtless aiding in the de- 

 hiscence of the anther, these cells increasing in size very rapidly 

 when the pollen approaches natunty. 



During the growth of the archesporium^ the tapetal cells may 

 divide radially ; but they soon become considerably modified in 

 appearance, and only nuclear divisions occur. The process of 

 nuclear activity in the tapetum are much as Strasburger^ has de- 

 scribed. The nuclei divide karyokinetically, Fig. 9, but no cell 

 plate is formed. In time the daughter nuclei may move together, 

 touch, and become flattened against each other, thus appeanng as 

 if in the process of direct division. In Bignonia, however, the 

 nuclei often remain apart throughout. 



It is of some interest to note the rate of growth in the cells of 

 the archesporium, beginning even with the outer periblem layer 

 which gives rise to the archesporium by its first periclinal divisions, 

 measuring the time by the development of the archesporial invest- 

 ments, etc. 



The following table indicates the measurements : 



Time. 



Akchespokial. 



rcriblem layer first differen- 

 tiated 



After the outer tapetum is 

 cut off. 



Immediately after the final 



division of the wall layer. 



During synapsis of the de- 



. finitive archesporial cells.. 



Cell. 



9.5-I3X1I-I3/Z 

 11-15X16.5-19// 



16. 5-19X22-27. 5 /X 



30-44X44-60 a 



Nucleus 



5-57/^ 

 8-g.6// 



li-14/i 

 ■ 16.5-18X16.5-22// 



Nucleolus. 



2.8/z 

 4-4. 8 // 



6.9// 



After synapsis there is httle growth in the pollen mother-cells 

 until divisions begin, although during the spirem stage the nucleo- 

 lus often attains a general diameter of 8 //, and a long diameter 

 even greater. 



Nucellns and Litc^iimcnt 



<b 



■ ■ T 



The ovule development conforms quite closely to that charac- 

 teristic of most Gamopetalae. The protuberance arising from the 



■^ Strasburgerj E. Theilungsvorgange der Zellkerne, 99-100. 1882. 



