EMBRYOLOGY OF THE АМЕМТТЕЕВЖ, 417 
though it had lost its outer coat, would in the normal state of things be safely housed or 
encysted in the tissue of the style. 
After observing this result of germination of pollen-grains, I was in some doubt as to 
how far it might be merely a pathological arrest of growth. I treated a number of 
fairly thick longitudinal median sections of the ovary of Carpinus with H,SO, in the 
hope that maceration of the surrounding tissue would bring into view any trace of the 
pollen-tubes in the stylar cylinder. Figs. 59 and 60 (Pl. LXXIT.) represent one of 
these macerated sections, taken from material gathered July 15, 1892; but I have as yet 
failed to obtain further evidence for the existence of a secondary pollen-grain or portion 
of tube encysted in the tissue of the style. 
Chalazal Route.—Leaving now the subject of the resting stage undergone by the 
pollen-tube, let us turn to a phenomenon which is less universal in Amentifers, and, so 
far as is at present known, is peculiar to the three groups Casuarines, Betulaceæ, and 
Corylacez. I refer to the route taken by the pollen-tube to gain access to the embryo- 
sac. 
Schacht, writing just forty years ago, claims to have observed a portion of the pollen- 
tube in the nucellus of Corylus. Не writes : “Several times have I seen in successful 
longitudinal sections a tubular cell in the tissue of the nucellus, which was united with 
a racemose body of cells lying in the'apex of the embryo-sac. The tubular cell, сиё off 
above, is the penetrated pollen-tube ” *. 
Here Schacht had probably made a very similar observation to that recorded by 
Hofmeister t in 1858 when he said, respecting Betula and Carpinus, that the cell-layers 
— 
covering the apex of the sac are tunnelled by the pollen-tube. | This statement has been 
a fruitful source of error. 
Treub quotes the passage as sufficient evidence for the normal course being pursued by 
the pollen-tube in these trees, and did not consider it necessary to investigate the matter 
further, although, as it appears, such a step would have led him to conclusions wholly 
different from those he drew from the literature on the subject. 
The pollen-tube does indeed in some instances (e.g. Alnus) tunnel the cell-layers 
which cover the apex of the embryo-sac, but it has, in such cases, reached these cell- 
layers by a route wholly аз abnormal as Treub has pointed out in the case of Casuarina. 
It descends from the tissue at the base of the stylar rudiments and, running Рея 
with the vascular bundle of the raphe, turns abruptly up into the nucellus on reaching 
its chalazal region (РІ. LXX. fig. 38). The base of the nucellus will be observed to lie 
in such a direction (figs. 32 and 34) that the pollen-tube following the trend of the cells 
in the neighbourhood of the vascular bundle of the raphe сш fail to find its way into 
the nucellus. This position of the base is gradually acquired by unequal Б 
* * Botanische Zeitung, 1854: Schacht, “ Beiträge zur Anatomie" &e. The “ пое Md ui Dd of the 
quotation refers probably to a group of three or four embryo-sacs which lie near the 5 t i m ш A 
р elei adie” tk (e Е UP MEUS ULL AM еее ania 
quently found in this region, and often strikingly suggestive of bits of — On the whole I cannot 
accept Schacht’s statement as evidence for the presence of a pollen-tube in this аі 
dung der Phanerogamen. 
t Pringsheim's * Jahrbuch, 1858: Hofmeister, « Embryobil АЕ 
SECOND SERIES.—BOTANY, VOL. III. 
