406 MORPHOLOGY. 



DICOTYLEDON*: M (continued). 

 Families. Species. 



Scropliularineae : 



Rhinanthea?. Pedicularis palustris, Melampyrum pra- 



tense. 



Veroniceas. Veronica hederaefolia, serpyllifolia. 

 Solaneae. Datura Tatula.* 

 Polemoniaceaa. Phlox paniculata. 

 Cuscutaceae. Cuscuta europsea. 



Gentianeaa. Gentiana lutea. 



Apocyneaa. Vinca rosea, minor, Nerium Oleander. 



Asclepiadese. Asclepias pulchra, Cynanchum nigrurn, 



Stapelia deflexa. Asterias. 



Campari ulaceaa. Campanula Medium*, rapunculoides. 



Compositae. Achillea Eupatorium, Hypoehceris radicata, 



Carduus nutans.* 



To the preceding list I must subjoin the following observations : 

 Pistia commutata I examined in dried specimens ; Pistia obcordata, 

 Cryptocoryne spiralis, and Podostemon ceratophyllum in specimens 

 which had been preserved in spirit. Otherwise the list is to be regarded 

 merely as an enumeration of certain examples, since, during the last 

 year or two I have not thought it worth the trouble to continue any 

 longer the formerly rigidly kept list concerning this one fact, which is 

 already put beyond a doubt by it ; and I must have named a great number 

 of additional families and species from memory, which I do not consider 

 to the purpose. The majority of the foregoing observations were made 

 in Berlin, and I made use of my uncle Horkel constantly as a testis 

 omni exceptione major, and therefore most of the facts are to be re- 

 garded as certified by him also, as he has already openly stated.* From 

 other quarters come the following confirmations. In the first place, Rob. 

 Brown for the Asclepiadacece and Orchidacece ; Wydler for the species of 

 Scrophularia, Griffith for the Santalacece. Brongniart's observations 

 also, of the pollen-tube hanging from the micropyles may now be added 

 to these, although he had a different view of their origin ; consequently 

 the families of the Cucurbitacece, Polygonacece, Euphorbiacece and Con- 

 volvulacecB ; further, Amici for Yucca gloriosa and many other plants 

 not specially named by him ; lastly, Meyen must be named, although, 

 in the whole of his somewhat confused exposition of fecundation and 

 formation of embryos, he constantly speaks of the universality of the 

 descent of the pollen-tube, but does not mention one single plant de- 

 finitely in which he had actually observed it : on the other hand, he cites 

 a large number of plants of the above-named families, as well as of some 

 others, in which he had observed the pollen-tube to enter into the mi- 

 cropyle. 



Easy as the observation is in some families, it is very difficult in 

 others ; not only the same circumstances occur here as in the tracing of 

 the canal of the style from the stigma to the cavity of the germen, but 

 it requires very much greater delicacy and skill in manipulation, to lay 

 the conducting tissue bare in large pieces in such a manner that it may 

 be conveniently separated under a simple microscope, and the pollen- 

 tubes be extricated. While in some plants, Orchidacece, Datura, (Eno- 



* Monatsbericbte der Berliner Academic dcr Wissenschaften, Aug. 18:36. 



