Vol. XXIII. No. lo.] 



POPULAE SCTET^CE NEWS. 



151 



^onje, Barnj, aijd Sardeij. 



THE NITROGEN BACTERIA. 

 Thirty years ago, Boussingault performed 

 his well-known experiment of planting seeds 

 in a soil devoid of nitrogen, and proving by 

 analysis of the seeds and the residting plants, 

 that no nitrogen was absorbed directly from 

 the air. Later, Berthelot and Andre dis- 

 covered that nitrogen accmmilates in culti- 

 vated soils through the action of bacteria, 

 which assimilate it from the air. Other 

 investigations by Hellriegel and Wilforth 

 showed that, in a soil free from nitrogen, 

 leginninous plants would not flourish when 

 watered with distilled water alone, but, if 

 w^ater containing the nitrogen bacteria was 

 used, or if the roots of the plants were inocu- 

 lated with the bacteria, the plant at once 

 began to grow and flourish, by absorbing 

 nitrogen from the air. 



Fig. I. Pea-pliint inocuhitcd with nitrogen Imcteria. Fip- 2. A 

 similar plant not inoculated. 



An interesting account of these investiga- 

 tions, together with a description of similar 

 experiments undertaken by himself, is given 

 in a recent number of La Nature by Profes- 

 sor E. Breal. He finds that the roots of 

 healthy leguminous plants, such as a pea, for 

 instance, are covered with numerous little 

 tubercles (Fig. 3.) When one of these tuber- 

 cles is crushed in a drop of water, and exam- 

 ined with the microscope, inmimerable bacte- 

 ria are discovered, and it is these bacteria 

 which are so necessary to the proper nourish- 

 ment of the plant. 



To prove this experimentally, Professor 

 Br^al planted two peas in separate pots in 

 an artificially prepared soil containing no 

 nitrogen ; one was watered with pure water, 

 the other with water containing the nitrogen 

 bacteria. Figs, i and 2 show the results 

 obtained. The plant inoculated with bacteria 



(Fig. i) attained a height of nearly five feet, 

 produced a large number of perfect seeds, 

 and its roots (Fig. 3) were found to be cov- 

 ered with the characteristic tubercles. The 

 condition of the other plant at the same age 

 is best shown by Fig. 3, and no tubercles 

 were found upon its roots. 



Fig. 3. Root of Fig. i, showing tubercles conUiining the 

 bacteria. 



The seed from which plant No. i was 

 grown contained nine milligrammes of nitro- 

 gen, as shown by the analysis of a similar pea 

 of equal weight, while the plant produced 

 from it contained 431 milligrammes of nitro- 

 gen. The increase, therefore, was 412 milli- 

 grammes, or 6.3 grains, which must 

 necessarily have been absorbed from the 

 air through the agency of the beneficent 

 nitrogen bacteria, — no small feat for these 

 little microscopic organisms to accomplish. 



These very important investigations will 

 aid in the solution of many practical agricul- 

 tural problems. It is well known to farmers, 

 for instance, that a crop of clover plowed 

 into the soil is in itself a most excellent fer- 

 tilizer. We can now see that this is largely 

 due to the pre.sence of the nitrogen bacteria, 

 which, while not directly enriching the soil 

 themselves, increase the amount of available 

 nitrogen present in it, and aid the growing 

 crops to assimilate it from the air. Modern 

 investigations are constantly adding to our 

 comprehension of the ver}' important func- 

 tions, both beneficial and harmful, of the 

 omnipresent bacteria, the very existence of 

 which was hardly known a quarter of a cen- 

 tury ago, and it is hard to say where the limits 

 of their functions will be found. 



There is a Beautiful Custom in some of the 

 northern parts of Europe. There the white poplar, 

 in good soil, increases a shilling in value every 

 year. The trees are generally cut down at the age 

 of twenty years, as they are then supposed to have 

 attained their full growth. When a daughter is 

 born in the family of a respectable farmer, the 

 father, as soon as the season will permit, plants a 

 thousand young trees, which are to constitute the 

 dowry of the maiden, "which grow as she grows 

 and increase in height and value as her virtues and, 

 beauty increase." 



[Original in The Popular Science N w$.] 

 COCO, CACAO, AND COCA. 



BY FRED'k LEROV SARGENT. 

 PART II. 



Cacao recommends itself to us chiefly as a luxury, 

 and as such it was highly prized by the ancient in- 

 habitants of Mexico and Central America, long 

 before the coming of Colinnbus. 



The Mexicans called the plant oacavatl, which, in 

 the language of the European invaders, became 

 cacao. The corruption of this into the commercial 

 name "cocoa" was probably favored by the fact that 

 the Mexican beverage from which our chocolate was 

 borrowed bore the name chocolatl. Linn;eus gave 

 to the plant the name Theohroma cacao, the generic 

 part being derived from the Greek, meaning "food 

 for the gods." 



Unlike the coco-nut, the cacao-plant is of all its 

 family (the Byttneriaceee) the only member of much 

 economic importance. All the other members of 

 the chocolate family are tropical or sub-tropical 

 plants, which have little more than a strictly botan- 

 ical interest. Their nearest relatives in temperate 

 regions are the mallows and lindens. 



Although the cacao-tree has been in cultivation for 

 a long period in Mexico, Central America, and the 

 West Indies, its native home appears to be the 

 forests of the Amazon and Orinoco basins, for here 

 it grows wild, and out of this region its occurrence 

 seems to be only under such circumstances as indi- 

 cate introduction by human agency. It is a curious 

 fact that all the evidences we have of the cultivation 

 of this plant prior to the arrival of the Spaniards, 

 relate to Mexico and Central America, and not at all 

 to South America. Humboldt accounts for this on 

 the supposition that the European settlers, having 

 learned the use of chocolate from the Mexicans, 

 established plantations of their own in South Amer- 

 ica, and thus started what is today one of the leading 

 industries of the region. Even at the time of Hum- 

 boldt's visit, eighty years ago, the number of trees in 

 full bearing, in Caracas, Nueva iJarcelona, Ven- 

 ezuela, Varinas, and Maracaybo, was estimated at 

 more than sixteen millions. 



The cultivation of cacao is so dependent upon a 

 climate of proper warmth and humidity, that 

 attempts to extend the industry to other tropica 1 

 countries have not met with much success. The 

 most notable exceptions are in the case of the 

 Phillippine and the Sunda Islands, where successful 

 plantations have been established. 



The plant is a shrub, or small tree, attaining the 

 height of sixteen to eighteen feet. In the wild state 

 it bears fruit the fourth year, but in cultivation the 

 first harvest is mostly delayed till the sixth or 

 seventh year after planting. When it is produced, 

 however, the fruit is much larger than that which 

 grows wild. The ripe cultivated fruit appears to be 

 not imlike a large cucumber or elongated squash, 

 pointed at the ends, about six to ten inches in 

 length, by three to five inches in thickness, and 

 with a yellowish leathery rind, which is strongly 

 marked with longitudinal ribs. Within is the soft, 

 pinkish, slightly acid pulp^ surrounding the numer- 

 ous (fifty to a himdrcd) oily seeds, which yield the 

 cacao or chocolate. 



The method of preparation is as follows : When 

 fully ripe the pods are gathered and left in a heap 

 for twenty-four hours. Then the seeds are taken 

 out and packed in a tight box, or put into trenches 

 or holes in the ground and covered with clay. 

 Thus confined, the seeds undergo a process of fer- 

 mentation, or "sweating," which is allowed to con- 

 tinue about two days. Upon the careful regulation 

 of this process depends in large part the fitness for 

 preservation and the flavor of the product, and great 



