THE HIGHER CRYPTOGAMIA. 339 



resemble a mixture of oil and albumen. If a spore be 

 crushed upon thin paper, it leaves behind a transparent stain. 



A few weeks after the spore has become free by the decay 

 of the walls of the sporangia, its interior begins to be filled 

 with cellular tissue. Sections afford no explanation as to 

 the nature of this cell-formation. If a spore which is not 

 yet entirely filled with closed parenchyma be crushed, its 

 contents become a formless pultaceous mass. If however 

 the exosporium be immersed for half an hour in a saturated 

 solution of glycerine, it becomes sufficiently transparent to 

 expose to view flatly-spherical accumulations of a granular 

 substance spread over the inner wall of the spore (PI. XL VI, 

 fig. 1). There can be no doubt that these masses of granu- 

 lar mucilage, which become confluent when the spore is 

 submitted to pressure, are newly-formed primordial cells, 

 i. e., naked primordial utricles ; and therefore that the for- 

 mation of the cellular tissue which fills the spore, i. e., of 

 the prothallium, is the result of free cell-formation. This 

 accords with the mode of origin of the endosperm of the 

 greater number of phsenogams, and especially with the de- 

 velopment of the albumen of the Coniferre. The formation 

 of rigid cell-membranes appears to commence for the first 

 time when the accumulated contents of the spore-cell have 

 become transformed into daughter-cells. 



This cell-formation probably commences in the apical 

 arch of the spore-cavity. When the parenchyma of the 

 spore is sufficiently firm to admit of longitudinal sections, 

 the cells of the apex of the prothallium are far smaller and 

 more numerous than those of its base. This leads to the 

 conclusion that a multiplication of the cells has commenced 

 at the apex some time previously, which multiplication does 

 not take place at the base until a much later period, and 

 then with far less activity. The contents of the cells of the 

 prothallium are not distinguishable from those of the ripe 

 spore. No nuclei are visible in the thick turbid fluid.* 



During the formation of the prothallium the inner mem- 



* The want of transparency of the milky cell-contents is so great, that even 

 in very thin sections it prevents the recognition of the boundaries of the cells 

 as long as the preparation lies in clean water. The addition of concentrated 

 solution of glycerine produces with greater rapidity a far more perfect trans- 

 parency than the chloride of calcium recommended by Mettenius, (' Beitr. zui* 

 Bot.,' Heft i, p. 11.) 



