485 
PHANEROGAMS. 
GROUP IV. 
PHANEROGAMS. 
The Alternation of Generations in Phanerogams is concealed in the formation 
of the Seed, which, at least in its earliest stage, consists of three parts: — (i) The 
Tesla, which is a part of the mother-plant; (2) The Endosperm^; and (3) The 
Embryo, which is the product of the development of the fertilised oosphere. 
In Vascular Cryptogams we have already seen the sexual generation which 
results directly from the spore, the prothallium, losing more and more of its character 
as an independent plant. In the Ferns, Equisetaceae, and Ophioglossaceae it grows 
independently of the spore, often for a considerable period ; in the Rhizocarpese and 
Ligulatse, where male and female spores are formed, it arises in the interior of the 
spore, the female prothallium still protruding, in the former group, out of the cavity 
of the macrospore, but remaining united with it; while in hoetes it fills up the 
interior of the macrospore as a mass of tissue which only bursts the cell-wall of 
the spore in order to render the archegonia accessible to the antherozoids. In the 
Cycadeae and Coniferae this metamorphosis is carried one step further; the pro- 
thallium^, which is now known as the Endosperm, remains during its whole existence 
enclosed in the macrospore or Embryo- sac ; it produces before fertilisation arche- 
gonium-like structures, the ' Corpuscula,' in which the oospheres arise. The pro- 
cesses which take place in the embryo-sac of Monocotyledons and Dicotyledons 
appear somewhat different, and bear a greater resemblance to what takes place in 
the macrospore of Selaginella. In this genus, besides the prothallium which pro- 
duces the archegonia, there arises subsequently, by free cell-formation, another tissue 
which fills up the rest of the space of the macrospore ; to this tissue the endosperm 
of Monocotyledons and Dicotyledons, which is formed by free cell- formation only 
after fertilisation, appears to correspond "\ If, therefore, the embryo-sac is the 
^ The only reason why the ripe seeds of many Dicotyledons do not contain any endosperm is 
because it has already been absorbed and supplanted by the rapidly growing embryo before the seeds 
become ripe ; while in others this absorption happens only on germination after the ripening of 
the seeds, i. e. on the unfolding of the embryo ; more rarely the formation of endosperm is from 
the first rudimentary. 
^ The analogy of the endosperm with the prothallium of the higher Cryptogams was first shown 
by Hofmeister (Vergleich. Untersuch. 1851), [Germination, Development, and Fructification of the 
Higher Cryptogamia, Ray Soc. 1862, p. 438]. 
^ Compare Pfeffer in Hanstein's Botanical Dissertations, Heft. IV. p. 24. The 'Antipodal 
Cells' in the embryo-sac of Angiosperms may probably be considered as a rudiment of the true 
prothallium. [According to Strasburger (Angiospermen und Gymnospermen, 1879) not only the 
antipodal cells and the egg-apparatus, but also the endosperm of the embryo -sac of Angiosperms, 
represent the prothallium (endosperm) of the Gymnosperms and of the Vascular Cryptogams. This 
view leaves the 'endosperm' of Selaginella without any representative in other groups of plants. 
Goebel has however expressed the opinion (Bot. Zeitg. 1880) that the endosperm of Selaginella 
corresponds to the antipodal cells of Angiosperms.] 
