TWE\TV-,SJJ\EXTJI AXXUAL MEF/PIXG. 155 



The contents of the spore consist of chlorophyl, starch granules, oil glob- 

 ules, mucus, and protoplasm. The spores of some species contain more oil 

 than others, and some are considerably more dense than others. 



The outer, thicker coat of the spore (primordial utricle, or moth cell) is 

 termed the exospore, and consists of differentiated protoplasm somewhat 

 similnr to cellulose. It is thicker in some species than others. The inner 

 part or contents of the spore is called the endospore. 



Spores when placed under favorable conditions, with moisture and 

 warmth, will germinate readily. First the exospore bursts and the endo- 

 spore protrudes and begins to divide, continuing the division and growth until 

 the long threads form the dense felt-like mat, resembling the light green 

 filaments of conferva, and forming a green film over rocks and walls. 



These green threads are termed the protonema, and correspond to the 

 prothallium of ferns. This is the first stage of the development of the sexual 

 generation, from the asexual spore. The long threads elongate by apical 

 growth, forming oblique septa and long cells; and giving rise to branches 

 just back of the septa. The septa are always inclined at different angles, 

 usually in three ways. 



The opposite side of the endospore sends out hyaline rhizoids, also 

 obliquely septate, which soon becomes brown. These penetrate the soil and 

 absorb nourishment: thus the protonema develops chlorophyl and supports 

 itself by assimilation. It soon forms leafy buds behind or below the septa or 

 node; the rhizoids develop below, firmly fixing it to the soil, where it soon 

 grows into the leafy axis, or what is ordinarily termed a moss, which is the 

 perfect stage of the sexual generation. (See plates 35 and 36.) 



The size and persistence of the protonema varies greatly in different 

 groups of mosses, it being very small in some species (less than a centimeter), 

 while in others it grows quite large, covering several centimeters with its 

 filaments, which live for some time, but it usually disappears when the leafy 

 axis is developed. In very minute mosses that live but a short time, the pro- 

 tonema grows vigorously, so that all stages of development may be present 

 on one individual, and genetically connected, as in Ephemerum, Micro- 

 mitrium, and others. (See plates.) 



The Sphagnaceae, Audreaeaceae and Tetraphidae differ from the typical 

 mosses in the structure of the sporogonia and in the formation of the pro- 

 tonema. The Sphagnaceae, when growing on a firm substratum, expand into 

 a flat plate of tissue, which branches at the margin, producing the leafy 

 stem from its upper surface. 



In Andreaea, according to Kuhn, the contents of the spore divide while 

 still within the closed exospore into four cells, forming a tissue similar to 

 that produced in the spores of some Hepaticae, as Radula and Fi'ullania, and 

 finally from one to two peripheral cells grow into filaments which extend over 

 the sub-stratum. (See "Sach's Text-book of Botany," pp. 361-363, and "Goe- 

 ble's Special Morphology," pp. 163-166.) 



Thus the protonema may develop in three ways, as above described. 

 Protonema may also be produced in numerous other ways, besides germi- 

 nating from spores, of which further detail will be given later. 



The rhizoids, or roots, are of three different kinds, the radical rhizoids, by 

 which the plant absorbs nourishment from the soil, protonemal rhizoids 

 serving the same purpose to the protonema, and lastly adventitious roots on 

 the stem and branches, termed tomentum; which are used for clinging and 

 absorbing moisture— chiefly the latter— and often forming a thick felt on stem 

 and branches, as in Bartramia and Dicranum. (See plates.) 



