LIFE OF TIIE PLANT-CELL. 109 



as, for instance, in Cycas and Abies, pore-canals also find their way 

 towards the free surface (vide pp. 45 50.). 



54. Peculiar changes also take place in the secretions, the 

 more solid secretions assuming definite forms. To these may be 

 referred the gelatinous envelop of many Alga; the intercellular 

 substance, the peculiar matter, which invests the spores and pollen- 

 grains ; and the matters secreted from the epidermis. 



Most Conferva, several Ulvce, &c., secrete a large quantity of gela- 

 tinous matter, which assumes a definite form, and thus frequently deter- 

 mines the figure of the whole plant, as in Chcetophora and Undina. In 

 most Confervce it constitutes a delicate uniform membrane investing the 

 whole plant ; in Rivularia, Chcetophora, Nostoc, &c., larger masses. It 

 is always wanting, however, in the spore, and is not formed except by 

 the vital activity of the self-multiplying cells.* 



In the same way a solid substance is secreted in the intercellular 

 passages : a similar secretion, of determinate form, is also found on the 

 epidermis. The subject of both these secretions will be entered upon 

 more fully hereafter ( 59. 63.). 



The most interesting and most complicated phenomenon, however, 

 still remains that of the peculiar investment of the spores and pollen- 

 grains. All spores (except those of the Algce, many Fungi, and some 

 Lichens), all pollen-grains (with the exception of those of plants which 

 flower under water), are constituted of the proper, essential cell, which 

 is formed as such, and a peculiar material investing it, which is simply 

 uniform or is furnished with warts, protuberances, spines, bands, or the 

 most extraordinary abnormal formations, disposed irregularly or with 

 the utmost mathematical regularity. The nature of this material differs 

 from all known assimilated vegetable substances in this respect : that it 

 is affected, according to Fritsche, not at all, according to others but 

 very slowly, by concentrated sulphuric acid, but is always rendered 

 more opaque, and sometimes of a purple-red colour. The matter itself 

 presents various colours, mostly yellow, though also blue, red, green, 

 brown, &c. It is a pure product of secretion of the spore, or pollen -cell. 

 I shall be obliged to say more about it afterwards, when speaking of the 

 pollen. For our best information respecting its chemical nature, but 

 especially with respect to its extraordinary forms, we are indebted to the 

 indefatigable and astonishing researches of Fritsche. f MohFs J opinion 

 upon this point that the external pollen-membrane is intercellular 

 substance, in which perfect cells or their beginnings (as granules) are 

 formed appears to be completely contradicted by Fritsche's, Meyen's , 

 my own, and Nageli's || investigations. The peculiar chemical nature 

 of the material appears at once to be opposed to any comparison of it 

 with the substances of which cells are formed. 



55. The peculiar relation in which the sap-currents stand 



* This condition has not been quite correctly comprehended by Mohl, Erlauterung 

 und Vertheidigung meiner Ansicht von der Structur der Pflanzensubstanz. Tubingen, 

 1836. In other respects he shows, as usual, distinguished powers of observation, 

 f Fritsche, Ueber den Pollen. Petersburg, 1837. 



\ Hugo Mohl, Beitriige zur Anatomic und Physiologic der Gewachse, Part I. ; und 

 Erlauterung und Vertheidigung, &c., p. 18. and elsewhere. 

 Physiologic, vol. iii. p. 146, et seq. 

 Zur Entwicklungsgesuhichte des Pollens, &c. 



