STRUCTURE.] GRIFFITH SCHLEIDEX. 355 



same relation to each other as the four angles of a cube. 



3. That the original number of cohering grains is in most 

 species of Inga, Acacia, and Mimosa, from eight to sixteen. 



4. That the external coat of the pollen-grain is not an uni- 

 form membrane, analogous to that of a simple cell, but an 

 organ composed of numerous cells like the integument of an 

 ovule, although it appears in some cases to be simply granular, 

 and in others to be almost homogeneous. This last idea is 

 sharply attacked by Mirbel (Ann.. Sc.; n. s., IV. 1.), who 

 insists upon the external skin of the pollen-grain being simple 

 in all cases. 



Mr. Griffith, in November 1836, published some curious 

 observations upon this subject, the result of which is, that in 

 Pardanthus chinensis the pollen is developed in the midst of 

 a solid grumous semiopaque mass, forming at a very early 

 stage the contents of one of the four cells of the anther; 

 that subsequently the grumous mass becomes cellular, the 

 cells having undergone some separation, and consisting of a 

 hyaline membrane containing a smaller mass of granular 

 molecular matter. Later still, each cell, which has acquired 

 an orange colour, presents traces of division into four, often 

 into three, very rarely into two portions, the division being 

 more distinct towards the circumference of each cell, and the 

 smaller masses being each enclosed in a proper cell, but 

 without having undergone any separation. Eventually each 

 of the divisions becomes a pollen-grain. " The young grains 

 are oblong-ovate, flattened on their contiguous or inner faces, 

 and open along the centre throughout the whole length of 

 their outer faces. They are even at this period reticulated, 

 and have rather a papillose appearance, and are lined by an 

 inner membrane in the form of a hyaline sac, which bulges 

 out slightly along the opening just mentioned." 



According to Schleiden, the difference between ordinary 

 pollen and that found in masses in Asclepiads and Orchids 

 consists in this, that the enveloping cells in common cases 

 are, and in the two others are not, absorbed. "This same 

 condition may be seen as a temporary stage in the develop- 

 ment of Picea and Abies, in the months of January and 

 February, in Pinus in February and March, in which a loose 



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