Biologie. 455 



'& 



tonnement des filaments dans les cultures des Rhizoctonia et de 

 Champignons tout differents, c'est-ä-dire dans des conditions oü il 

 ne saurait etre question d'action humorale, de phenomenes defensifs, 

 de cellules capables d'imposer aux Champignons des modes de Ve- 

 getation anormaux avant de les detruire par phagoc3'tose. 



P. Vuillemin. 



Holm, T., Biologie plan t-tj^pes. (Ontario nat. Sc. Bull. V. 

 p. 9—22. 1909.) 



While Humboldt was the first to call attention to the existence 

 of distinct types of Vegetation, described b}" him from a very general, 

 but highly esthetic point of view, several authors of a more recent 

 date have attempted to analyse these types with the object of clas- 

 sitying their components from a morphological or biological view- 

 point. However the Classification of such biological types has proved 

 a most difficult task, and the difficulty seems to depend upon the 

 fact, that even if certain biologic t5^pes maj' be predominant in the 

 various climates, and stations, we nevertheless observe that a 

 multitude of others, though less conspicuous and less frequent, do 

 occur with these in the same places. In the present paper the author 

 describes several types of North American plants in order to demon- 

 strate some examples of the peculiar Variation in equipment pos- 

 sessed \)\ closely allied species or genera, as seedling, and as 

 mature plants. but without making any attempt to classify these 

 within certain frames of structure. 



Attention is called to Ricinus, which occurs as an annual in 

 the temperate climates, but as an arborescent in the tropics; to 

 Cypenis ßavescens, Arahis lyrata and others, which vary from an- 

 nual to perennial. Several species of Ranunciihis represent at the 

 seedling-stage a type of growth very distinct from that of the mature 

 plant, readily noticeable in R. pnsilhis, of which the seedling is an 

 aquatic with floating leaves and submersed stems, while the mature 

 plant is terrestrial, and with the habit in general of a terrestrial. 

 Seedlings of monopodial Carices do not differ from those sympodial, 

 and it requires several years before the final, and very distinct type 

 of ramification becoms apparent. 



In regard to the occurrence of distinct structures possessed by 

 allied species, the Convolvulaceae offer a good example; we notice 

 the extensively creeping and freely rooting aerial stem of Ipomoea 

 acetosaefolia in contrast with the trailing, sometimes twining. but 

 not rooting stems of /. pandurata; furthermore the erect or ascen- 

 ding stems of /. leptophylla with narrow, linear leaves. In the two 

 last species the primary root persists attaining an enormous size 

 and weight aggregating to nearly a hundred pounds. In Convolvidiis , 

 C. spithaniaeus has very short, never twining stems, and its roots 

 produce an abundance of root-shoots, a t3'pe very distinct from C. 

 sepiiini, C. Soldanella, and C longipes. Several interesting tj^pes 

 occur among the Cniciferae, for instance in Dentaria. In this genus 

 the rhizome is generally more or less tuberous, and creeping, gla- 

 brous or toothed. In D. tenella small hairy tubers are developed 

 upon the long subterranean petioles, while in D. bulbifera the aerial 

 stems are bulbiferous. In Cardamine the annual and perennial species 

 show ver}"- interesting structures in the same respect. 



Much richer in tj'pes is, however, the small family Portidaceae, 

 of which the species of Claytonia contain annual, and perennial 



