ANGIOSPERMS, 
557 
really bilocular anthers of Asclepiadese and the octilocular ones of many Mimoseas. 
Sometimes again the anther-lobes open at the apex by a pore which results simply 
from the destruction of a small portion of tissue at this spot (Hofmeister). In other 
respects we still want a detailed and comparative investigation of these processes, 
which are very various and of great physiological importance; only the additional 
remark need be made here, that it is very important from a systematic point of view 
whether the anthers open inwards towards the gynaeceum (introrse), or outwards 
(extrorse), the difference depending on the position of the suture and hence on that of 
the pollen-sacs on the inner or outer side of the filament. 
In several families of Monocotyledons and Dicotyledons more or less con- 
siderable deviations ^ occur from the course of development of the pollen and 
from its final structure which has been here described. Naias and Zostera deviate 
only to this extent, that no thickening of the wall of the mother-cells takes place, 
and that the pollen-cells themselves are very thin-walled, acquiring in Zostera a very 
strange appearance from assuming, instead of the ordinary rounded form, that of long 
thin tubes lying parallel to one another in the anther. The deviations are more 
considerable in the formation of compound pollen-grains. The origin of these is 
either that only the four daughter-cells (pollen-cells) of one mother-cell remain 
more or less closely united, like the pollen-tetrads (four-fold grains) of some 
Orchideae, Fourcroya, Typha^ Anona, Rhododendron, Sec; or the whole product of 
one primary mother-cell remains unseparated and forms a mass of pollen consisting 
of eight, twelve, sixteen, thirty-two, or sixty-four connected pollen-cells, as in many 
Mimoseae and Acacieae^. In these cases the cuticle or extine is more strongly 
developed on the outer surface of the daughter-cells lying at the circumference of 
the mass, and covers the whole as a continuous skin ; while only thin ridges of the 
cuticle project from this skin inwards between the separate cells. In the various 
sections of Orchidese every gradation occurs from the ordinary separate pollen-grains 
of Cypripedium, through the four-fold grains of Neoitia, to the Ophrydese, where all 
the pollen-grains which are formed from each primary mother-cell remain united, 
and thus a number of pollen-masses lie in one pollen-sac ; and finally to the PoUinia 
of the Cerorchideae, where all the pollen-grains of a pollen-sac remain united into 
a cellular mass. In this case, as in the Asclepiadeae with only bilocular anthers, 
where the grains of each pollen-sac are firmly united by a waxy substance, it is 
obvious that the pollen cannot be dispersed, nor can the pollen-masses fall out spon- 
taneously from the anthers; but the flower is provided with very peculiar con- 
trivances by means of which insects in search of honey extract from the pollen-sac 
the pollinia or the masses of pollen which are glued together, and again get rid of 
them on to the stigmas of other flowers of the same species (see Book III on Sexual 
Reproduction). 
The Female Sexual Organs or Gyncßcewn ^ (Pistil) of the flowers of Angiosperms 
^ In reference to what follows compare Hofmeister, Neue Beiträge, pt, II, (Abhand der könig. 
Sachs. Gesellsch, VII); also Reichenbach, De pollinis Orchidearum genesi, Leipzig 1852; and 
Rosanoff, Ueber den Pollen der Mimosen (Jahrb. für wissensch. Bot. VI. p. 441). 
^ In many Mimosese the anther is, according to Rosanoff, octilocular, two pairs of small loculi 
being formed in each anther-lobe; the pollen-cells of each pollen-sac remain united into a mass. 
^ Compare with this Payer's view (Organogenic de la fleur, p. 725), which differs in some 
essential points. 
