16 



BOTANY 



PART I 



the vacuole walls can be formed anew, but are nevertheless very 

 important parts of the protoplast, since they determine the taking up 

 of substances. They are semipermeable membranes, i.e. they allow 

 water to pass, but are impermeable or only slightly permeable to 

 many other substances. 



Living protoplasm has frequently a foam -like structure. In 

 dividing protoplasts fine filaments may appear which cease to be 

 evident in the resting condition of the cell. It is not known whether 

 the cytoplasm has a still finer internal structure which is not visible. 

 When fixed and stained, a reticulate or honeycomb - like structure 

 with embedded granules is formed as in other coagulated colloidal 

 solutions. 



In addition to the structures alluded to above, there have recently been 

 demonstrated in the cytoplasm of both embryonic and permanent cells certain 

 filamentous, spindle-shaped or dumb-bell-shaped structures. 

 These are best seen after special fixation and staining, and 

 agree so closely with the CHONDRIOSOMES (mitochondria) of 

 embryonic animal cells that they have been given the same 

 name ( u ). Probably they include bodies of various nature 

 such as minute vacuoles, filamentous structures in the cyto- 

 plasm, young chromatophores, etc. They have been observed 

 in some Mosses in the embryonic cells beside the chromato- 

 phores, and also in the Fungi. 



2. The Nucleus ( 12 ) has as a rule a spherical, 

 oval, or lenticular form, but in long cells may be 

 correspondingly elongated. In embryonic cells its 

 diameter may amount to two-thirds of the total 

 diameter of the protoplast. In full-grown cells of 

 the permanent tissue, on the other hand, the 

 nucleus is much less conspicuous, since it has not 

 increased in size. Large nuclei are found in most 

 Conifers, in some Monocotyledons, and in the 

 Ranunculaceae and Loranthaceae among the Di- 

 cotyledons. Secretory cells are as a rule provided 

 .-- W u ith especially large nuclei. On the other hand, 

 gus, Hyphoioma fasti- the nuclei of the majority of Fungi (Fig. 6) and of 

 cuiare, containing five ma ny Siphoneae are very small. 



While the cells of the Cormophytes are almost 

 always uninucleate, in the Thallophytes, on the 

 contrary, multinucleate cells are by no means infrequent. In many 

 Fungi (Fig. 6), and in the Siphoneae among the Alg ae > they are 

 the rule. The whole plant is then composed either of but one single 

 multinucleate cell, which may be extensively branched and exhibit 

 a complicated external form (Fig. 346), or it may consist of a large 

 number of multinucleate cells, forming together one organism. Thus, 

 on suitable treatment, several nuclei may be detected in the peripheral 



nuclei, (x 500. After 

 KNIEP.) 



