DR. SCHACHT, ON THE MICROSCOPE. 



223 



swell up and escape from the mother-cell ; when this takes place, cells 

 called special mother-cells (which exist also in certain other plants, as, for 

 instance, Lavetera) are found to be present. 



Fig. 109. 



Fig. 111. 



112. 



Fig. 113. 



Figs 112 and 113 represent mother-cells of Picea vulgaris, which have 

 become quadrilolucar by the formation of special mother-cells ; the young 

 pollen-grains having been swollen by water 

 have escaped from the mother-cells. These 

 special mother-cells, which were first observed 

 by Nageli, are nothing more than a primary 

 layer of cellulose secreted by the i^riinordial 

 utricle of the pollen-cell, the pollen-cell itself 

 having originated by division of the primordial 

 utricle. This layer of cellulose, like the mother- 

 cell, is afterwards either absorbed by the pollen-grains themselves, or appro- 

 priated in some other way to the perfecting of them. When the four young 

 pollen-cells of Picea escape from their mother-cells, the latter appear, to a 

 certain extent, to be divided by the special mother-cells into four partitions. 

 (^See fig. 113.) The young pollen-grain is then generally no longer round ; 

 tlie two lateral excrescences, which at a subsequent period characterize 

 the pollen-grain of Picea, Abies, and Larix, are already more or less per- 

 ceptible. 



Fig. 114. Fig. 115. Fig. 116. 





Figs. 114 and 115 represent young pollen-grains at this period, showing 

 the commencement of the formation of the two lateral excrescences. Fig. 

 116 shows a young pollen-grain of Picea vulgaris, somewhat further de- 

 veloped, seen imder water ; (.r) is the place of egress of the pollen-tube. 

 A laige nucleus, surrounded by granular matter, lies apparentlj^ free in 

 the middle of each pollen-grain. From this time the lateral ^jrotube ranees 

 continue to increase in size, the cuticle, i. e. the outer membrane of the 

 pollen-grain, which does not consist of cellulose, becomes stronger and 

 stronger, and delicate markings, streaks, and lines appear upon it, esjiecially 

 upon the protuberances. 



Figs. 117 and 118 represent respectively ripe pollen-grains of Abies 

 jaectinata and Picea vulgaris which have been soaked for half an hour in 

 oil of lemons ; in each figure («) is the terminal cell of the cellular bodj' ; 

 (&) and (c) the pedicel-cells ; in both (c) has the appearance of a fissure, as 

 is the case in Larix ; (x) is the place of egress for the pollen-tube. The 

 processes going on in the interior of the pollen-grain are at this time con- 

 cealed, more or less, by the granular contents ; nevertheless, I believe that 

 in Abies I have seen the formation of a cell-membrane, that is the origin 

 of a cell, around the central nucleus. When tlie anther of the above- 



