PHANEUOGAMIA : FLOWERS. 



403 



252 



boyeau, pollen-tubes, budetti pollinici). In the three first-named fa- 

 milies this penetrates immediately into the nuclear papilla ; in the 

 rest it follows the conducting cellular tissue, sometimes growing 

 forth on its surface, sometimes penetrating through its loosened 

 cells, till it reaches the cavity of the germen, and here penetrates 

 through the micropyle, or immediately into the nuclear papilla 

 of the seed-bud. 



"Whether and how the embryo originates 

 from the pollen-tube is in the first place 

 dependant on the question, whether and 

 how the pollen-tube in each case reaches 

 the micropyle and the papilla of the 

 nucleus ; and it is important for the esta- 

 blishment of the facts to separate the two 

 questions completely from each other. The 

 first question, how the pollen -cell deports 

 itself on the stigma, I believe I may an- 

 swer as in the paragraph, for all Phanero- 

 gamia, without exception ; on this point, I 

 think, the facts now lying before us can 

 leave no doubt ; it were rather to be wished 

 that all our inductions in Botany were as 

 well supported. For the illustration of 

 this process may serve a preparation of 

 Helianthemum denticulatum (fig. 252.), in 

 which plant I have not imfrequently ex- 

 tracted the pollen-tube free, in unbroken 

 continuity from the pollen-grain to the 

 seed-bud. I refer also to Plate IV. figs. 

 1 3., with their explanation. However, 

 it appears to me to be to the purpose to 

 give a review of the observations on which 

 my statements are founded. In the fol- 

 lowing plants of the following families I 

 have traced the pollen-tube from the 

 stigma into the micropyle ; in those marked 

 with an asterisk I have frequent, isolated 

 the pollen-tube, in complete, unbroken 

 continuity from the pollen-granule to the seed-bud. 



Families. 



Abietinece.* 

 Cupressineae.* 



GYMNO8PER1LE, 



Species. 



Larix europaea, Abies pectinata, alba, ex- 

 celsa, Pinus sylvestris, uncinata. 



Taxus baccata. Jnniperus communis, sativa, 

 virginiana, Thuja orientalis, Callitris 

 quadrivalvis. 



fiB Helianthemum rlcnticnfafinn. The pistil, in longitudinal section. a, Germen ; 

 6, style ; c, stigma ; rl, pollen-granules, the tubes of which descend in the germen as far 

 as the seed-buds. 



n i) 2 



