14.  However, I take up first, and with best hope, Dr. Asa Gray, who tells me (Art. 211) that pith consists of parenchyma, ’which is at first gorged with sap,’ but that many stems expand so rapidly that their pith is torn into a mere lining or into horizontal plates; and that as the stem grows older, the pith becomes dry and light, and is ’then of no farther use to the plant.’  But of what use it ever was, we are not informed; and the Doctor makes us his bow, so far as the professed article on pith goes; but, farther on, I find in his account of ‘Sap-wood,’ (Art. 224.) that in the germinating plantlet, the sap ’ascends first through the parenchyma, especially through its central portion or pith.’  Whereby we are led back to our old question, what sap is, and where it comes from, with the now superadded question, whether the young pith is a mere succulent sponge, or an active power, and constructive mechanism, nourished by the abundant sap:  as Columella has it,—­

“Naturali enim spiritu omne alimentum virentis quasi quaedam anima, per medullam trunci veluti per siphonem, trahitur in summum."[41]

As none of these authors make any mention of a communication between the cells of the pith, I conclude that the sap they are filled with is taken up by them, and used to construct their own thickening tissue.

15.  Next, I take Balfour’s ‘Structural Botany,’ and by his index, under the word ‘Pith,’ am referred to his articles 8, 72, and 75.  In article 8, neither the word pith, nor any expression alluding to it, occurs.

In article 72, the stem of an outlaid tree is defined as consisting of ’pith, fibro-vascular and [42] woody tissue, medullary rays, bark, and epidermis.’

A more detailed statement follows, illustrated by a figure surrounded by twenty-three letters—­namely, two b s, three c s, four e s, three f s, one l, four m s, three p s, one r, and two v s.

Eighteen or twenty minute sputters of dots may, with a good lens, be discerned to proceed from this alphabet, and to stop at various points, or lose themselves in the texture, of the represented wood.  And, knowing now something of the matter beforehand, guessing a little more, and gleaning the rest with my finest glass, I achieve the elucidation of the figure, to the following extent, explicable without letters at all, by my more simple drawing, Figure 25.

16. (1) The inner circle full of little cells, diminishing in size towards the outside, represents the pith, ’very large at this period of the growth’—­(the first year, we are told in next page,) and ’very large’—­he means in proportion to the rest of the branch. How large he does not say, in his text, but states, in his note, that the figure is magnified 26 diameters.  I have drawn mine by the more convenient multiplier of 30, and given the real size at B, according to Balfour:—­but without believing him to be right.  I never saw a maple stem of the first year so small.