BOTANICAL SUIJJECTS. 



239 



lu the evolution of pollen, however we may eall its various 

 stages by different names, we cannot lose sight of the main fact 

 that evorv vegetable eell is only a repetition, with mcdifi cation^ 

 of the original protophytoUy or unicellular body, which is the 

 basis of all the aggregations we see, and for which a whole 

 dictionary of terms has been invented. 



I have already stated that pollen originates in the mother-cells, 

 each of which contains four pollen-grains, and therefore these 

 tetrads are comparable to the tetraspores of cryptogams. When, 

 however, I throw my mind back to Dallinger's monads, I find 

 simple nucleated cells moving about, which eventually ripen into 

 pollen -grains and ovules, or, what comes to the same thing, male 

 and female cells, which, after conjugation to form a bigger cell, 

 burst and let out a multitude of spores ; therefore, the quaternary 

 sub-division of the mother-cells in these cases would appear of little 

 significance. 



According to my interpretation then, the glands on the petiole 

 of the cherry leaf have stored up in them potentially^ either leaf- 

 teeth, or ovules, or ijollen. "What governs the evolution of the 

 one in jH'eference of the other, from the same cellular basis, we do 

 not know. 



The histological method will not help us nuicli, for we see 

 that an anther in its young stage consists simply of uniform 

 cells, some outer, some inner. It is only after some time that the 

 development of mother-cells begins to make its appearance. In 

 these eventually develop pollen-grains, in groups of four. 



The homology of the petiole glands can only be cleared 

 by induction, based on comparison, position, and teratological 

 transformations. 



If a part, which is normally an anther, sometimes develops 

 into a leaf, or leaflet, or petal, we have no choice but to believe 

 that the anther has stored up in it potentially the teeth of a 

 leaf. 



If we find that the teeth of a cherry leaf .sometimes amalgamate 

 into a gland similar to those on the petiole, we logically infer 

 that the glands have stored up in them potentially the teeth of 

 leaflets, and that they are aborted leaflets converted into what 

 we call glands, in the same way that stipules are aborted 

 leaflets. 



