Beer, Development of the poUen grain and antlier of some Onagraceae. 301 



itself and tlie pollen-wall and, in' all probability, the latter derives 

 tlie necessary materials for its growth from this source. 



Unfortunately I could gain no knownledge whatsoever of 

 the chemical nature of this liquid. 



In the tapetuni we can also observe evidences of nietabolic 

 activity but I can find nothing to show that any of the material 

 which is being formed there is leaving the cells, on the con- 

 trary there is reason to believe that an accumulation of sub- 

 stance is taking place. 



In the very young pollen grain ^) the first wall appears as 

 a Single homogeneous lamella but when the grain has grown 

 and measures about 40 f/ across we can indistinctly recognise a 

 structural differentiation in the outer membrane. 



AVhen the diameter of the poUen grain has increased still 

 further (to about 55 to 60 fi) its first membrane can be clearly 

 Seen to consist of a thin, outer homogeneous layer and an inner 

 "rodlet''' layer (Stäbchenschicht or Anschlußlameila-). 



The growth of this membrane recalls Strasburger's ^) 

 description of the first pollen-wall of ÄUhaca rosea which, at a 

 certain stage, was seen to consist of three lamellae: a middle 

 "rodlet" layer (Anschlußlameila) which is bounded peripherally 

 by two homogeneous layers. Of these the innermost lamella 

 soon ceases to grow and becomes gradually more attenuated 

 until it is lost sight of altogether ; the two other lamella increase 

 in thickness and the "rodlets" can be very clearly studied in 

 older stages. A thickening layer is developed within the first 

 pollen membrane of Älthaea. 



In Oenothera the first wall is so thin during its early deve- 

 lopment that I have not been able to determine whether the 

 "rodlet" layer is ever bounded internally by an inner homogeneous 

 lamella ; it is certain, however, that by the time the pollen grain 

 has reached 55 to 60 // in diameter every trace of it has vanished. 



The first pollen-wall now grows more rapidly in surface 

 than the secondary thickening layer beneath it and consequentty 

 it becomes separated from that layer at all parts and only re- 

 mains firmly fixed to the interstitial bodies. The continuation of 

 this unequal growth in surface gradually throws the outer wall 

 into irregulär and sinuous folds. Botli primary and secondary 

 layers of the waU have meanwhile undergone a change in their 

 chemical Constitution and have become more or less completely 

 cuticularised. The secondary layer no longer gives a pure violet 

 colour with a Solution of lodine in potassium iodide but this 

 has changed fii'st to a violet - brown and then to a pure brown 

 reaction. 



1) This description of the jiolleii-wall applies both to Oenoth. longiftora 

 and to Oen. biennis unless specially stated to the contrary. The nieasure- 

 nients more particulary refer to O. hicnnix ])nt tlie dimensions are onh^ very 

 slightlj'', different in 0. lo>/fj//lora. 



-) Strasbur f;er. -'Die pflanzlichen Zellhäute". (Pringsh. Jahrl). f. wiss 

 Bot. Ed. XXXI. 18i>8. p. 551.) 



3) 1. c. p. 555. 



