240 CONTRIBUTIONS TO
in its individual development that its wall is thickened by secondary deposits.
3. The cytoblasts also remain persistent in the pollen-granules in some rare instances ; such is the case in some, perhaps in all the Abietinæ. The lenticular cytoblast has already been observed by Fritsche in Larix europæa, but the true nature of it was not recognised.
4, Lastly, many hairs, particularly such as exhibit motions of the sap within their cells, retain the cytoblasts (c, f, fig. 25). It is at the same time remarkable, and a proof of the close relation which the cytoblast bears to the whole vital activity of the cell, that the little currents which frequently cover the entire wall like a network, always proceed from and return to it, and that when in statu integro it is never situated without the currents (fig. 25).
I have observed the above-described development of the cells throughout its entire course in the albumen of Chamædorea schiedeana, Phormium tenax, Fritillaria pyrenaica, Tulipa sylvestris, Elymus arenarius, Secale cereale, Leucoji spec., Abies excelsa, Larix europæa, Euphorbia pallida, Ricinus leucocarpa, Momordica elaterium, and in the embryonal extremity of the pollen-tube of Linum pallescens, Ginothera crassipes, and many other plants.
It was in the summer of 1837, after this treatise had been written, that I first began to examine the Leguminosæ, and found to my surprise that these plants, so constantly investigated and everywhere employed as illustrations for the history of vegetable development, afforded the most beautiful and ready opportunities for the study of this process, which had been overlooked by all observers. No one, however, had considered the saccharine fluid contained in the embryonal sac as worthy of examination.
Without exactly tracing the entire course of the formation of the cells through all its details, I found the cell-nuclei, previous to the appearance of the cells, floating loose in the fluid in very many plants. Finally, I have not met with a single example of newly-developed cellular tissue, the cambium excepted, in which the cytoblasts were wanting. I therefore consider that I am justified in assuming the process above described to be the universal law for the formation of the vegetable cellular tissue in the Phanerogamia.
