10 FIRST GROUP. 



APOGAMY IN THE THALLOPHYTES. It was stated above, that in the 

 formaiion of the fruit in the Ascomycetes organs make their appearance, which are 

 obviously analogous with the male and female organs of other Thallophytes, but 

 which have no longer any sexual function. This loss of the procreative faculty is 

 termed by De Bary apogamy, and is by no means uncommon among the 

 Thallophytes. Thus it occasionally happens with several of the Zygomycetes 

 {Syzygiies) that the conjugating branches do not unite, but nevertheless they each 

 form at their free extremity a cell which has the properties of a zygospore. The 

 apogamy is still more striking in the case of the Saprolegnieae, and is constant 

 throughout their entire cycle of affinity. The form of the sexual organs agrees with 

 that of the Peronosporeae (Fig. 4). The antheridia in many cases put out their 

 fertilisation-tubes, but these remain closed and emit no fertilising substance. Never- 

 theless the oospores mature in the usual manner. Other individuals have antheridia, 

 but these put out no tubes; others again have neither antheridial branches nor 

 antheridia, and yet the oospores are developed. In the two last cases we have not 

 only apogamy but a suppression of the sexual organs, which goes still further in the 

 Ascomycetes ; for in many of these neither antheridial branch nor archicarp can be 

 distinguished ; the fructifications are formed simply by the sprouting and interweaving 

 of hyphal twigs of similar form, some of which are transformed later into ascogenous 

 filaments. A parallel case is known also among the Chlorophyceae : the oospores 

 of Chara crinita mature in the normal manner without being fertilised by sperma- 

 tozoids. Finally in many Fungi, especially in the great division of the Basidiomycetes, 

 the formation of the fructification is altogether suppressed ; they have only asexual 

 organs of reproduction. The formation of these organs will now be described. 



II. EORMATIOW OF ASEXUAL REPRODUCTIVE ORGANS. Besides 

 spores, the direct or indirect products of sexual organs, the Thallophytes usually possess 

 an extremely fruitful source of propagation in their brood-cells, which are not the 

 products directly or indirectly of sexual organs. Only a few Thallophytes, such as the 

 Conjugatae, Sphacropka, and the Fucaceae, have no brood-cells, but sexually produced 

 spores alone. 



Brood-cells or gonidia^ are formed on the thallus often without preliminary 

 preparation, the whole contents of certain cells of the thallus renewing themselves, or 

 dividing also at the same time, and so producing one or more reproductive cells which 

 separate from the parent-plant. In other cases special stalks or receptacles are 

 formed on the thallus, whose exclusive function it is to produce gonidia, either by 

 abstriction of the extremities of special branches {stilogonidia in Piptocephalis, 

 PenicilUwn and others), or by free cell-formation inside large cells (endogonidia in 

 Saprolegnieae, Vaucheria, Mucorineae). In many cases, especially in many Fungi, 

 reproduction is eflfected almost exclusively by such brood-cells, the normal completion 



' All the reproductive cells of the Thallophytes were formerly termed ' spores ' without refer- 

 ence to their mode of origin. To remove the confusion thus caused, Sachs proposed that only the 

 reproductive cells, which were the direct or indirect result of a sexual act, zygospores, oospores, 

 carpospores, ascospores, &c., should be termed spores, and that the asexual organs of reproduction 

 should be called gonidia or conidia, a term common among the Fungi from Kov'ia, dust. But it 

 would appear that the old nomenclature is not to be set aside, being supported by a number of 

 related terms, such as sporangia and others. 



