416 HOFMEISTER, ON 



tissue of the endosperm. This has been often observed in 

 Pinus canadensis. In Taxus it often destroys the entire 

 uppermost part of the endosperm ; on the other hand the 

 four cells which close up the corpusculum which is about 

 to be impregnated, are at first only slightly pushed apart 

 from one another, by the protrusion by the pollen-tube of 

 a short prolongation which passes between their detached 

 edges and up to the outer wall of the corpusculum (PL 

 LXIV, figs. 1,2). These cells do not disappear until a later 

 period, after the formation of the pro-embryo ; they often last 

 for a very long time (PL LXIII, fig. 13). Juniperus and 

 Thuja (PL LXV, figs. 2, 3, 9, 10,) behave in "a similar 

 manner. In the Abietineae, on the other hand, the cells above 

 the corpuscula are destroyed immediately after the pollen- 

 tube has reached them (PL LX, fig. 9 ; PL LXI, fig. 1 ; 

 PL LXII, figs. 2, 3). Its end attaches itself to the outer 

 wall of the corpusculum ; in Pinus canadensis it then 

 often expands considerably in breadth (PL LXII, fig. 3). 

 With this process in most cases, its penetration terminates ; 

 more rarely it breaks through the wall of the corpusculum 

 and grows into it for a short distance. This happens 

 regularly in Pinus Larix, and tolerably frequently in Pinus 

 canadensis (PL LXI, figs. 13, 14; PL LXII, fig. 2).* 



Free spherical cells are often developed in the interior of 

 the ends of those pollen-tubes of the Coniferse which 

 penetrate up to, or into the corpusculum. In the Abietineae 

 the observation of them is often rendered difficult by the 

 large number of co-existent starch-granules, but even here 

 undoubted instances of the presence of cellular formations 

 in the pollen-tubes may easily be seen. The pollen-tube of 

 Pinus canadensis when it has penetrated into the corpus- 

 culum usually contains — in addition to granules of starch 

 and mucilage — several (2, 4, or even 8) sharply defined 

 spherical balls of finely granular protoplasm floating freely 

 in the interior of the tube (PL LXIII, fig. 2). In some of 

 these corpuscula I saw, close under the end of the pollen- 

 tube but not in contact with it, a free oval cell differing 

 from the germinal vesicles which — still in the same state as 

 before the arrival of the pollen-tube — filled the rest of the 



* Many such cases are figured by Pineau, 'Ann. d. Sc.' iii. ser., vol. xi, 

 pi. vi, fig. 4 ; and by Schacht, ' Entw. des Pflanzen-erabryon,' pi. xi, fig. 5 — 7. 



