| 
| “SMents and in 
1898] ORIENTATION OF THE PLANT EGG 395 
thecalyptra. In one particular, however, there is pretty gener- 
ily in the Marchantiaceze of higher rank than Sphzrocarpus a 
modification of the primitive position of the sporophyte with 
tlerence to the horizon. Instead of being erect it is inverted 
more or less completely. This is due to the inversion of the 
uchegone which, although developed dorsally on the thallus, is 
airied into a ventral position by displacements of growth, so 
that the neck of the archegone points towards the substratum. 
As the archegone is carried to an inverted position the egg must 
ako be unless it rotates in the venter, a process which does not 
lake place in ontogeny although apparently it does in phylogeny. 
fig. 3 shows in diagrammatic fashion the 
is segmentation stage of the March- 
ma egg with the epibasal hemisphere 
stown black as before and now directed B B 
‘ownward instead of upward. In either 
= however, whether the embryo of 
otal or Marchantia be consid- 
ia be noted that the epibasal 
re ae is pesentially the distal nee: 
ea while the hypobasal is 
a ¥ va proximal. In Bryo- 
“strong distinction arises between these differently situated 
oe i pteridophytic types of embryogeny where the 
. 2 frequently rotated to one side or even inverted in thre 
_ sone under ecological stress, it is always possible to dis- 
fom hag segment which is the homologue of the originally 
trith the that and this, whatever its position in the re 
i. = lus or the horizon, is termed the epibasal sigh 
te seen e 1on of an epibasal and hypobasal segment Is there 
© be one of phylogeny rather than of embryogeny- 
Fic. 3.— Embryo of 
Marchantia. 
E 
"ryogeny of Anthoceros.—While important work on the 
*Poro 
MPhyte of Anthoceros was accomplished by Schacht? in 
> Be: 
itr, a ‘ 
Ue. Zeit Bggy atickelungsgesch. der Frucht und Spore von Anthoceros laevis. 
"497. 1850, 
