MUCORINI. 235 



Florida as early as February. In searching for conjugating specimens 

 only the yellow and brown masses of filaments need be examined, as 

 the process never takes place in the bright green ones. 



314. In the genera Mesocarpus and Pleurocarpus the 

 conjugation is slightly different from that described above. 

 The conjugating tube, which is much longer, becomes di- 

 lated midway between the two filaments, and in this the 

 contents of the two cells unite and form a zygospore. This 

 difference has been considered by some botanists to be of 

 sufficient importance to set off these genera in a group allied 

 to, but distinct from, the Zygnemaceae. When they are so 

 set off they constitute the Mesocarpece ; but it is altogether 

 probable that they are to be considered rather as a subdivi- 

 sion of the Zygnemacese than as a distinct order. 



Mesocarpus scalaris is our most common species. In general appear- 

 ance it resembles the previously mentioned species, but its chlorophyll 

 is not so regularly arranged. 



315. Order Mucorini. The Moulds are saprophytic and 

 sometimes parasitic plants ; they are composed of long 

 branching filaments (hyphm), which always form a more or 

 less felted mass, the mycelium ; when first formed the hyphae 

 are continuous, but afterward septa are formed in them at 

 irregular intervals. The protoplasmic contents of the hy- 

 phae are more or less granular, but they never develop chlo- 

 rophyll. The cell-walls are colorless, except in the fruiting 

 hyphae, which are usually dark colored or smoky (fuliginous). 

 The mycelium sometimes develops exclusively in the inte- 

 rior of the nutrient medium ; in other cases it develops 

 partly in the medium and partly in the air. In some species 

 the mycelium may occasionally attach itself to the hyphse 

 of other plants of the same order, and even to nearly related 

 species, and derive nourishment parasitically from them. It 

 is doubtful, however, whether any Moulds are entirely para- 

 sitic, and so far as parasitism occurs it appears to be con- 

 fined to narrow limits ; none, so far as known, are parasitic 

 upon higher plants. 



316. The reproduction of Moulds is asexual and sexual. 

 In the asexual reproduction the mycelium sends up erect 



